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Reserve for Loss and Loss Expense Reserve for Loss and Loss Expense (Claims Development) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Claims Development [Line Items]
Reserve for loss and loss expense	$ 3,771,240,000	$ 3,691,719,000
Incurred loss and loss expense for claims occurring in the prior years	(39,192,000)	(65,768,000)	$ (69,009,000)
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	7,727,861,000
Net outstanding liabilities	10,417,364,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,041,694,000
Short-duration Insurance Contracts, Accident Year 2008 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	860,745,000	853,769,000	839,392,000	$ 819,280,000	$ 798,996,000	$ 764,196,000	$ 690,016,000	$ 609,851,000	$ 489,633,000	$ 286,314,000
Net outstanding liabilities	923,978,000	926,017,000	931,785,000	927,958,000	936,975,000	947,306,000	964,862,000	990,931,000	988,584,000	957,247,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 41,791,000
Short-duration Insurance Contracts, Number of Reported Claims	85,338
Short-duration Insurance Contracts, Accident Year 2009 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 784,713,000	775,885,000	760,589,000	736,100,000	695,249,000	634,902,000	540,982,000	442,417,000	277,275,000
Net outstanding liabilities	848,413,000	853,401,000	857,960,000	869,927,000	870,057,000	883,590,000	916,691,000	941,972,000	920,143,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 41,937,000
Short-duration Insurance Contracts, Number of Reported Claims	85,575
Short-duration Insurance Contracts, Accident Year 2010 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 835,532,000	823,770,000	803,773,000	773,536,000	704,895,000	625,229,000	509,910,000	328,826,000
Net outstanding liabilities	907,074,000	915,131,000	922,404,000	943,118,000	956,600,000	977,959,000	973,742,000	950,114,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 50,293,000
Short-duration Insurance Contracts, Number of Reported Claims	94,258
Short-duration Insurance Contracts, Accident Year 2011 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 924,111,000	901,801,000	852,202,000	782,655,000	692,730,000	585,867,000	391,944,000
Net outstanding liabilities	1,019,351,000	1,023,726,000	1,033,518,000	1,056,107,000	1,062,233,000	1,061,667,000	1,042,576,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 63,891,000
Short-duration Insurance Contracts, Number of Reported Claims	104,500
Short-duration Insurance Contracts, Accident Year 2012 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 856,195,000	810,135,000	743,742,000	651,544,000	555,819,000	378,067,000
Net outstanding liabilities	973,644,000	973,089,000	998,028,000	1,020,655,000	1,071,290,000	1,065,437,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 77,542,000
Short-duration Insurance Contracts, Number of Reported Claims	103,745
Short-duration Insurance Contracts, Accident Year 2013 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 833,823,000	748,758,000	644,475,000	518,872,000	335,956,000
Net outstanding liabilities	1,002,316,000	1,021,007,000	1,047,230,000	1,062,045,000	1,044,142,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 116,449,000
Short-duration Insurance Contracts, Number of Reported Claims	90,755
Short-duration Insurance Contracts, Accident Year 2014 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 855,959,000	736,154,000	614,075,000	405,898,000
Net outstanding liabilities	1,124,014,000	1,146,990,000	1,133,798,000	1,107,513,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 171,913,000
Short-duration Insurance Contracts, Number of Reported Claims	94,375
Short-duration Insurance Contracts, Accident Year 2015 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 725,385,000	581,203,000	376,641,000
Net outstanding liabilities	1,144,830,000	1,130,513,000	1,114,081,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 256,758,000
Short-duration Insurance Contracts, Number of Reported Claims	92,891
Short-duration Insurance Contracts, Accident Year 2016 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 617,958,000	387,272,000
Net outstanding liabilities	1,203,634,000	1,188,608,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 416,010,000
Short-duration Insurance Contracts, Number of Reported Claims	92,191
Short-duration Insurance Contracts, Accident Year 2017 [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 433,440,000
Net outstanding liabilities	1,270,110,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 634,863,000
Short-duration Insurance Contracts, Number of Reported Claims	88,941
Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 352,192,000
Standard Commercial Lines [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,262,217,000
Net outstanding liabilities	2,273,761,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	1,092,058,000
Standard Commercial Lines [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,272,395,000
Net outstanding liabilities	1,941,745,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	916,471,000
Standard Commercial Lines [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,677,641,000
Net outstanding liabilities	2,137,614,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	464,131,000
Standard Commercial Lines [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	401,363,000
Net outstanding liabilities	477,234,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	83,163,000
Standard Commercial Lines [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,080,689,000
Net outstanding liabilities	1,130,739,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	50,300,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	198,360,000	194,257,000	186,896,000	176,873,000	166,394,000	151,055,000	113,088,000	82,421,000	45,595,000	16,397,000
Net outstanding liabilities	219,617,000	221,203,000	221,640,000	219,551,000	224,236,000	233,712,000	234,770,000	243,536,000	243,755,000	250,239,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 14,326,000
Short-duration Insurance Contracts, Number of Reported Claims	13,769,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 198,512,000	195,962,000	191,265,000	188,206,000	180,556,000	171,403,000	158,083,000	139,144,000	100,678,000	39,628,000
Net outstanding liabilities	238,218,000	238,836,000	243,512,000	244,100,000	245,993,000	241,921,000	250,423,000	255,810,000	243,186,000	219,616,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 25,993,000
Short-duration Insurance Contracts, Number of Reported Claims	14,401,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 181,979,000	181,779,000	180,779,000	175,244,000	173,795,000	166,487,000	151,741,000	130,857,000	104,711,000	69,053,000
Net outstanding liabilities	183,151,000	183,618,000	183,736,000	180,902,000	182,785,000	187,417,000	187,100,000	190,349,000	195,823,000	196,370,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 736,000
Short-duration Insurance Contracts, Number of Reported Claims	24,129
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 30,873,000	30,873,000	29,778,000	28,589,000	28,660,000	28,026,000	25,738,000	24,449,000	21,765,000	15,019,000
Net outstanding liabilities	31,065,000	30,967,000	31,340,000	31,066,000	29,793,000	30,250,000	32,974,000	39,334,000	38,986,000	39,660,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 192,000
Short-duration Insurance Contracts, Number of Reported Claims	3,258,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 101,032,000	101,034,000	100,868,000	100,908,000	100,752,000	100,213,000	99,288,000	100,465,000	98,921,000	68,211,000
Net outstanding liabilities	101,054,000	101,043,000	100,881,000	101,043,000	101,702,000	101,265,000	101,470,000	101,436,000	102,860,000	97,578,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,000
Short-duration Insurance Contracts, Number of Reported Claims	7,604,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 180,621,000	176,316,000	166,767,000	151,920,000	130,554,000	103,213,000	64,970,000	37,143,000	14,346,000
Net outstanding liabilities	201,568,000	205,741,000	206,387,000	211,243,000	212,947,000	223,146,000	233,530,000	241,625,000	237,913,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 17,629,000
Short-duration Insurance Contracts, Number of Reported Claims	13,841,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 167,894,000	164,336,000	160,529,000	154,726,000	145,417,000	133,116,000	117,019,000	87,299,000	37,885,000
Net outstanding liabilities	208,142,000	208,611,000	212,536,000	216,992,000	210,756,000	210,109,000	213,036,000	215,946,000	197,504,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 22,575,000
Short-duration Insurance Contracts, Number of Reported Claims	12,217,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 160,013,000	159,723,000	158,303,000	155,560,000	149,949,000	137,564,000	113,697,000	94,406,000	63,126,000
Net outstanding liabilities	161,300,000	161,923,000	161,251,000	162,911,000	166,682,000	169,858,000	182,724,000	191,079,000	199,541,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 897,000
Short-duration Insurance Contracts, Number of Reported Claims	24,652
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 43,547,000	43,448,000	43,358,000	42,895,000	40,052,000	36,073,000	32,689,000	29,612,000	18,915,000
Net outstanding liabilities	43,933,000	44,273,000	44,299,000	44,938,000	43,553,000	43,828,000	46,645,000	51,762,000	48,535,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 272,000
Short-duration Insurance Contracts, Number of Reported Claims	3,474,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 80,405,000	80,509,000	80,529,000	80,352,000	80,251,000	80,894,000	80,433,000	78,695,000	59,933,000
Net outstanding liabilities	80,416,000	80,545,000	80,558,000	80,455,000	80,774,000	82,014,000	82,025,000	82,124,000	82,619,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4,000
Short-duration Insurance Contracts, Number of Reported Claims	7,009,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 178,179,000	172,394,000	161,487,000	143,360,000	113,050,000	80,018,000	46,201,000	15,726,000
Net outstanding liabilities	202,394,000	208,968,000	211,619,000	222,328,000	237,154,000	242,499,000	228,680,000	215,208,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 18,403,000
Short-duration Insurance Contracts, Number of Reported Claims	12,672,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 162,796,000	158,078,000	153,795,000	149,086,000	137,184,000	122,442,000	93,281,000	46,795,000
Net outstanding liabilities	204,423,000	208,155,000	212,448,000	214,916,000	211,030,000	212,815,000	214,469,000	198,371,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 28,964,000
Short-duration Insurance Contracts, Number of Reported Claims	12,184,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 169,793,000	169,100,000	167,227,000	163,513,000	146,913,000	128,015,000	99,254,000	68,098,000
Net outstanding liabilities	173,471,000	173,157,000	172,969,000	179,854,000	181,923,000	187,778,000	189,305,000	187,562,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,491,000
Short-duration Insurance Contracts, Number of Reported Claims	25,301
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 40,395,000	40,279,000	38,900,000	37,819,000	34,705,000	31,027,000	28,131,000	20,821,000
Net outstanding liabilities	41,197,000	41,239,000	40,581,000	40,899,000	39,915,000	42,408,000	49,285,000	53,669,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 697,000
Short-duration Insurance Contracts, Number of Reported Claims	3,917,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 95,150,000	95,156,000	95,147,000	95,270,000	95,111,000	94,602,000	91,918,000	69,543,000
Net outstanding liabilities	95,155,000	95,178,000	95,363,000	95,530,000	96,127,000	97,386,000	96,851,000	105,647,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5,000
Short-duration Insurance Contracts, Number of Reported Claims	7,667,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 170,525,000	159,768,000	135,377,000	102,978,000	73,643,000	42,692,000	13,924,000
Net outstanding liabilities	212,011,000	211,196,000	217,256,000	230,785,000	239,480,000	228,720,000	227,769,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 25,729,000
Short-duration Insurance Contracts, Number of Reported Claims	11,579,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 154,320,000	149,269,000	139,232,000	134,646,000	118,847,000	90,836,000	42,941,000
Net outstanding liabilities	200,674,000	205,708,000	210,591,000	215,114,000	214,743,000	218,973,000	205,238,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 32,881,000
Short-duration Insurance Contracts, Number of Reported Claims	11,845,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 170,000,000	166,082,000	157,291,000	142,507,000	121,576,000	99,196,000	69,849,000
Net outstanding liabilities	174,514,000	174,882,000	172,617,000	178,421,000	182,325,000	183,044,000	174,006,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,937,000
Short-duration Insurance Contracts, Number of Reported Claims	25,272
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 57,045,000	55,856,000	52,114,000	46,444,000	41,011,000	37,362,000	27,884,000
Net outstanding liabilities	58,456,000	58,966,000	59,256,000	58,242,000	51,047,000	57,083,000	54,469,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,080,000
Short-duration Insurance Contracts, Number of Reported Claims	4,959,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 131,089,000	131,115,000	131,060,000	130,681,000	129,579,000	127,580,000	94,538,000
Net outstanding liabilities	131,049,000	131,113,000	131,353,000	131,282,000	130,942,000	131,667,000	136,954,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4,000
Short-duration Insurance Contracts, Number of Reported Claims	9,036,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 130,866,000	109,448,000	89,008,000	56,580,000	35,241,000	13,030,000
Net outstanding liabilities	175,268,000	175,305,000	194,144,000	215,083,000	245,561,000	238,979,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 27,702,000
Short-duration Insurance Contracts, Number of Reported Claims	9,922,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 139,477,000	132,052,000	122,755,000	108,211,000	86,909,000	40,911,000
Net outstanding liabilities	187,359,000	188,596,000	195,197,000	199,360,000	208,036,000	203,864,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 36,233,000
Short-duration Insurance Contracts, Number of Reported Claims	11,605,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 176,656,000	168,114,000	148,669,000	127,235,000	105,371,000	73,316,000
Net outstanding liabilities	186,128,000	184,367,000	184,289,000	183,527,000	191,947,000	179,551,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3,880,000
Short-duration Insurance Contracts, Number of Reported Claims	23,889
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 40,627,000	38,766,000	37,215,000	35,089,000	31,833,000	22,199,000
Net outstanding liabilities	43,747,000	44,077,000	44,172,000	46,303,000	48,029,000	54,342,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 756,000
Short-duration Insurance Contracts, Number of Reported Claims	5,540,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 116,625,000	116,291,000	114,699,000	111,503,000	108,834,000	81,528,000
Net outstanding liabilities	117,170,000	117,102,000	116,658,000	115,375,000	114,224,000	118,464,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 24,000
Short-duration Insurance Contracts, Number of Reported Claims	8,514,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 139,114,000	104,587,000	72,127,000	35,113,000	12,789,000
Net outstanding liabilities	210,785,000	225,709,000	239,776,000	251,421,000	250,609,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 53,014,000
Short-duration Insurance Contracts, Number of Reported Claims	10,226,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 118,669,000	109,739,000	96,376,000	74,568,000	36,829,000
Net outstanding liabilities	166,662,000	173,160,000	187,658,000	194,318,000	199,794,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 34,776,000
Short-duration Insurance Contracts, Number of Reported Claims	11,366,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 189,626,000	169,850,000	140,015,000	109,893,000	76,469,000
Net outstanding liabilities	210,410,000	207,994,000	209,197,000	205,282,000	188,289,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 8,258,000
Short-duration Insurance Contracts, Number of Reported Claims	25,392
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 37,993,000	34,760,000	30,845,000	26,592,000	17,412,000
Net outstanding liabilities	41,369,000	40,624,000	41,005,000	42,618,000	49,617,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3,192,000
Short-duration Insurance Contracts, Number of Reported Claims	3,479,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 90,840,000	90,350,000	90,446,000	87,874,000	60,244,000
Net outstanding liabilities	90,436,000	90,005,000	90,103,000	90,639,000	88,101,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 42,000
Short-duration Insurance Contracts, Number of Reported Claims	5,709,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 121,969,000	79,972,000	46,825,000	14,901,000
Net outstanding liabilities	239,333,000	257,132,000	249,946,000	244,312,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 80,168,000
Short-duration Insurance Contracts, Number of Reported Claims	10,391,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 113,626,000	100,876,000	78,944,000	35,924,000
Net outstanding liabilities	172,515,000	182,579,000	187,065,000	199,346,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 42,869,000
Short-duration Insurance Contracts, Number of Reported Claims	10,482,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 180,701,000	148,884,000	117,169,000	80,810,000
Net outstanding liabilities	219,925,000	216,824,000	212,725,000	200,534,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 19,053,000
Short-duration Insurance Contracts, Number of Reported Claims	27,338
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 49,460,000	44,911,000	40,584,000	28,914,000
Net outstanding liabilities	59,806,000	62,548,000	60,949,000	55,962,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5,952,000
Short-duration Insurance Contracts, Number of Reported Claims	4,054,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 137,883,000	136,634,000	132,909,000	101,131,000
Net outstanding liabilities	138,751,000	136,820,000	136,249,000	141,192,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 126,000
Short-duration Insurance Contracts, Number of Reported Claims	6,512,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 78,668,000	39,978,000	14,665,000
Net outstanding liabilities	246,990,000	245,710,000	254,720,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 124,639,000
Short-duration Insurance Contracts, Number of Reported Claims	9,987,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 98,195,000	77,320,000	33,857,000
Net outstanding liabilities	183,604,000	194,639,000	193,729,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 42,287,000
Short-duration Insurance Contracts, Number of Reported Claims	10,530,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 175,866,000	132,260,000	91,347,000
Net outstanding liabilities	253,074,000	240,958,000	220,994,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 36,137,000
Short-duration Insurance Contracts, Number of Reported Claims	28,818
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 42,710,000	36,014,000	24,189,000
Net outstanding liabilities	57,245,000	53,768,000	52,871,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 10,256,000
Short-duration Insurance Contracts, Number of Reported Claims	3,913,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 109,829,000	106,182,000	79,048,000
Net outstanding liabilities	111,750,000	109,513,000	110,270,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 261,000
Short-duration Insurance Contracts, Number of Reported Claims	6,398,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 46,549,000	15,684,000
Net outstanding liabilities	272,048,000	277,214,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 178,904,000
Short-duration Insurance Contracts, Number of Reported Claims	9,617,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 78,531,000	34,525,000
Net outstanding liabilities	184,946,000	196,774,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 70,424,000
Short-duration Insurance Contracts, Number of Reported Claims	10,509,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 155,720,000	106,022,000
Net outstanding liabilities	274,367,000	255,187,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 71,303,000
Short-duration Insurance Contracts, Number of Reported Claims	30,480
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 36,848,000	24,655,000
Net outstanding liabilities	53,792,000	52,335,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 11,938,000
Short-duration Insurance Contracts, Number of Reported Claims	3,757,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 118,789,000	83,966,000
Net outstanding liabilities	126,185,000	121,927,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 804,000
Short-duration Insurance Contracts, Number of Reported Claims	6,686,000,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 17,366,000
Net outstanding liabilities	293,747,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 249,085,000
Short-duration Insurance Contracts, Number of Reported Claims	8,194,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 40,375,000
Net outstanding liabilities	195,202,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 112,086,000
Short-duration Insurance Contracts, Number of Reported Claims	10,182,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 117,287,000
Net outstanding liabilities	301,274,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 132,814,000
Short-duration Insurance Contracts, Number of Reported Claims	30,187
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 21,865,000
Net outstanding liabilities	46,624,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 15,252,000
Short-duration Insurance Contracts, Number of Reported Claims	3,462,000
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 99,047,000
Net outstanding liabilities	138,773,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 8,794,000
Short-duration Insurance Contracts, Number of Reported Claims	6,358,000,000
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | General Liability [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 80,514,000
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	247,121,000
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	4,158,000
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	7,292,000
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	250,000
Standard Personal Lines [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	962,602,000
Net outstanding liabilities	1,049,297,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	92,557,000
Standard Personal Lines [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	648,479,000
Net outstanding liabilities	673,804,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	30,728,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	98,810,000	98,668,000	98,604,000	98,174,000	97,723,000	95,932,000	91,834,000	84,715,000	73,194,000	50,396,000
Net outstanding liabilities	99,270,000	99,116,000	99,255,000	99,686,000	99,912,000	100,213,000	103,934,000	106,842,000	106,999,000	100,311,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 191,000
Short-duration Insurance Contracts, Number of Reported Claims	16,042
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 37,928,000	37,930,000	37,939,000	37,933,000	37,837,000	37,763,000	37,086,000	36,271,000	33,535,000	21,277,000
Net outstanding liabilities	38,038,000	38,045,000	38,042,000	38,111,000	38,410,000	38,062,000	39,203,000	39,342,000	41,747,000	$ 41,224,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 56,000
Short-duration Insurance Contracts, Number of Reported Claims	5,139,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 103,009,000	102,437,000	102,322,000	102,187,000	100,566,000	96,229,000	86,431,000	71,911,000	51,039,000
Net outstanding liabilities	103,348,000	103,412,000	103,393,000	103,866,000	104,734,000	103,908,000	105,033,000	103,319,000	93,808,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 191,000
Short-duration Insurance Contracts, Number of Reported Claims	17,346
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 40,269,000	40,189,000	39,907,000	39,819,000	39,731,000	39,342,000	38,078,000	36,965,000	28,299,000
Net outstanding liabilities	40,451,000	40,457,000	40,465,000	40,400,000	61,927,000	40,313,000	42,609,000	44,511,000	$ 47,636,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 73,000
Short-duration Insurance Contracts, Number of Reported Claims	5,633,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 106,733,000	106,453,000	105,849,000	104,061,000	101,540,000	95,300,000	82,490,000	58,786,000
Net outstanding liabilities	107,054,000	107,224,000	107,405,000	107,490,000	109,515,000	112,346,000	110,075,000	103,340,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 222,000
Short-duration Insurance Contracts, Number of Reported Claims	20,822
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 62,272,000	62,241,000	62,227,000	62,155,000	61,106,000	60,295,000	58,638,000	43,699,000
Net outstanding liabilities	62,392,000	62,339,000	62,402,000	62,462,000	97,761,000	63,285,000	67,525,000	$ 68,373,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 84,000
Short-duration Insurance Contracts, Number of Reported Claims	9,131,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 113,551,000	112,732,000	111,085,000	105,068,000	93,878,000	82,102,000	61,323,000
Net outstanding liabilities	113,988,000	113,830,000	114,241,000	112,993,000	113,686,000	116,164,000	113,232,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 284,000
Short-duration Insurance Contracts, Number of Reported Claims	22,700
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 94,007,000	93,720,000	93,312,000	92,185,000	91,718,000	89,963,000	71,668,000
Net outstanding liabilities	94,378,000	94,183,000	94,543,000	94,167,000	82,744,000	98,211,000	103,804,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 159,000
Short-duration Insurance Contracts, Number of Reported Claims	15,106,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 109,355,000	107,890,000	102,977,000	94,842,000	82,729,000	63,704,000
Net outstanding liabilities	110,300,000	110,294,000	109,324,000	109,832,000	114,921,000	113,771,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 728,000
Short-duration Insurance Contracts, Number of Reported Claims	22,332
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 85,562,000	85,196,000	84,250,000	82,720,000	79,584,000	69,056,000
Net outstanding liabilities	86,330,000	86,271,000	86,667,000	86,560,000	82,745,000	87,260,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 180,000
Short-duration Insurance Contracts, Number of Reported Claims	16,936,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 105,131,000	100,528,000	92,637,000	80,861,000	61,384,000
Net outstanding liabilities	107,759,000	106,703,000	106,225,000	109,620,000	108,417,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 851,000
Short-duration Insurance Contracts, Number of Reported Claims	22,371
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 71,776,000	69,775,000	67,838,000	65,528,000	50,664,000
Net outstanding liabilities	71,714,000	72,145,000	71,494,000	72,528,000	73,670,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 284,000
Short-duration Insurance Contracts, Number of Reported Claims	7,747,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 99,173,000	92,589,000	83,739,000	62,519,000
Net outstanding liabilities	107,452,000	106,757,000	109,325,000	102,250,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,554,000
Short-duration Insurance Contracts, Number of Reported Claims	22,499
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 81,664,000	79,751,000	76,007,000	61,561,000
Net outstanding liabilities	83,844,000	83,637,000	82,461,000	80,111,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,146,000
Short-duration Insurance Contracts, Number of Reported Claims	8,762,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 87,163,000	76,470,000	58,725,000
Net outstanding liabilities	100,214,000	99,698,000	96,387,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 6,541,000
Short-duration Insurance Contracts, Number of Reported Claims	20,840
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 72,202,000	70,078,000	52,589,000
Net outstanding liabilities	76,559,000	76,400,000	76,637,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,744,000
Short-duration Insurance Contracts, Number of Reported Claims	7,724,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 76,823,000	57,961,000
Net outstanding liabilities	98,032,000	92,727,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 11,651,000
Short-duration Insurance Contracts, Number of Reported Claims	19,747
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 57,333,000	42,252,000
Net outstanding liabilities	60,931,000	60,105,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,067,000
Short-duration Insurance Contracts, Number of Reported Claims	6,820,000,000
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 62,854,000
Net outstanding liabilities	101,880,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 22,284,000
Short-duration Insurance Contracts, Number of Reported Claims	19,818
Standard Personal Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Homeowners [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 45,466,000
Net outstanding liabilities	59,167,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5,315,000
Short-duration Insurance Contracts, Number of Reported Claims	6,651,000,000
Standard Personal Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 5,862,000
Standard Personal Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | Homeowners [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	5,403,000
E&S Lines [Member]
Claims Development [Line Items]
Reserve for loss and loss expense						15,000,000
E&S Lines [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	192,604,000
Net outstanding liabilities	471,628,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	279,023,000
E&S Lines [Member] | Commercial Property [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	13,519,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	97,000	92,000	79,000	80,000	70,000	24,000	0
Net outstanding liabilities	119,000	(162,000)	52,000	119,000	146,000	169,000	92,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0
Short-duration Insurance Contracts, Number of Reported Claims	35,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 737,000	709,000	626,000	605,000	431,000	198,000	0
Net outstanding liabilities	737,000	96,000	710,000	728,000	938,000	1,053,000	885,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0
Short-duration Insurance Contracts, Number of Reported Claims	274,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 4,610,000	4,513,000	4,078,000	3,574,000	2,570,000	1,218,000	0
Net outstanding liabilities	4,932,000	3,055,000	3,831,000	4,299,000	3,369,000	4,106,000	3,294,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0
Short-duration Insurance Contracts, Number of Reported Claims	804,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 10,256,000	9,912,000	9,954,000	6,445,000	3,200,000	806,000	0
Net outstanding liabilities	10,228,000	9,652,000	10,273,000	12,207,000	9,853,000	7,102,000	$ 8,127,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 361,000
Short-duration Insurance Contracts, Number of Reported Claims	1,316,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 36,278,000	32,343,000	25,064,000	16,430,000	7,914,000	3,722,000
Net outstanding liabilities	45,988,000	46,165,000	46,149,000	43,175,000	42,621,000	$ 42,367,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 7,313,000
Short-duration Insurance Contracts, Number of Reported Claims	2,006,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 46,108,000	35,200,000	21,980,000	9,470,000	2,715,000
Net outstanding liabilities	67,647,000	69,112,000	67,099,000	60,309,000	$ 55,468,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 15,326,000
Short-duration Insurance Contracts, Number of Reported Claims	2,219,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 43,877,000	25,571,000	12,234,000	2,353,000
Net outstanding liabilities	71,719,000	69,929,000	63,505,000	$ 55,316,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 18,224,000
Short-duration Insurance Contracts, Number of Reported Claims	1,987,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 29,389,000	13,057,000	3,036,000
Net outstanding liabilities	82,404,000	76,432,000	$ 75,498,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 32,909,000
Short-duration Insurance Contracts, Number of Reported Claims	2,606,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 16,195,000	3,720,000
Net outstanding liabilities	96,416,000	$ 94,451,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 65,489,000
Short-duration Insurance Contracts, Number of Reported Claims	2,454,000,000
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | General Liability [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 5,057,000
Net outstanding liabilities	91,438,000
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 79,354,000
Short-duration Insurance Contracts, Number of Reported Claims	1,760,000,000
E&S Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2008 [Member] | General Liability [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 0

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