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Schedule I - Summay of Investments - Other Than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Amortized Cost or Cost	$ 5,020,045
Carrying Amount	5,089,269
Held-to-maturity Securities [Member]
Amortized Cost or Cost	201,054
Fair Value	209,544
Carrying Amount	201,354
Held-to-maturity Securities [Member] | Obligations of States and Political Subdivisions [Member]
Amortized Cost or Cost	175,269
Fair Value	181,880
Carrying Amount	176,117
Held-to-maturity Securities [Member] | Public utilities [Member]
Amortized Cost or Cost	9,637
Fair Value	10,662
Carrying Amount	9,647
Held-to-maturity Securities [Member] | All Other Corporate Securities [Member]
Amortized Cost or Cost	10,591
Fair Value	11,353
Carrying Amount	10,396
Held-to-maturity Securities [Member] | Asset-backed Securities [Member]
Amortized Cost or Cost	1,030
Fair Value	1,028
Carrying Amount	910
Held-to-maturity Securities [Member] | Commercial Mortgage-backed Securities (CMBS) [Member]
Amortized Cost or Cost	4,527
Fair Value	4,621
Carrying Amount	4,284
AFS Fixed Income Securities [Member]
Amortized Cost or Cost	4,352,514
Fair Value	4,408,203
Carrying Amount	4,408,203
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
Amortized Cost or Cost	99,485
Fair Value	104,115
Carrying Amount	104,115
AFS Fixed Income Securities [Member] | Foreign Government Obligations [Member]
Amortized Cost or Cost	14,885
Fair Value	15,181
Carrying Amount	15,181
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
Amortized Cost or Cost	1,314,779
Fair Value	1,359,142
Carrying Amount	1,359,142
AFS Fixed Income Securities [Member] | Public utilities [Member]
Amortized Cost or Cost	156,786
Fair Value	157,270
Carrying Amount	157,270
AFS Fixed Income Securities [Member] | All Other Corporate Securities [Member]
Amortized Cost or Cost	1,735,510
Fair Value	1,742,912
Carrying Amount	1,742,912
AFS Fixed Income Securities [Member] | Asset-backed Securities [Member]
Amortized Cost or Cost	244,541
Fair Value	244,154
Carrying Amount	244,154
AFS Fixed Income Securities [Member] | Commercial Mortgage-backed Securities (CMBS) [Member]
Amortized Cost or Cost	245,252
Fair Value	243,592
Carrying Amount	243,592
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities (RMBS) [Member]
Amortized Cost or Cost	541,276
Fair Value	541,837
Carrying Amount	541,837
Common Stock [Member]
Amortized Cost or Cost	181,991
Fair Value	194,789
Carrying Amount	194,789
Common Stock [Member] | Public Utility, Equities [Member]
Amortized Cost or Cost	9,106
Fair Value	10,080
Carrying Amount	10,080
Common Stock [Member] | Banks, Trust and Insurance Companies [Member]
Amortized Cost or Cost	23,622
Fair Value	23,696
Carrying Amount	23,696
Common Stock [Member] | Industrial, Miscellaneous, and All Other [Member]
Amortized Cost or Cost	149,263
Fair Value	161,013
Carrying Amount	161,013
Preferred Stock [Member]
Amortized Cost or Cost	11,825
Fair Value	12,262
Carrying Amount	12,262
Preferred Stock [Member] | Banks, Trust and Insurance Companies [Member]
Amortized Cost or Cost	11,825
Fair Value	12,262
Carrying Amount	12,262
Equity Securities [Member]
Amortized Cost or Cost	193,816
Fair Value	207,051
Carrying Amount	207,051
Short-term Investments [Member]
Amortized Cost or Cost	194,819
Fair Value	194,819
Carrying Amount	194,819
Other Investments [Member]
Amortized Cost or Cost	77,842
Carrying Amount	$ 77,842

X

- Definition

This element represents the carrying (reported) amount of the entity's investments as of the balance sheet date. This amount may represent the individual investment's or group of similar investments' original cost, fair value, or such other amount at which the investment is shown in the entity's balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

This item represents the original cost of the entity's investments including investments in equity securities and, as to fixed maturities, original cost reduced by repayments and adjusted for amortization of premiums or accrual of discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010

+ Details

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X

- Definition

This item represents the reported amount of the entity's investments measured at fair value. Fair value is the price that would be received to sell an investment in an orderly transaction between market participants at the balance sheet [measurement] date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010

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