Schedule I - Summay of Investments - Other Than Investments in Related Parties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Amortized Cost or Cost	$ 4,683,151
Carrying Amount	4,806,834
Held-to-maturity Securities [Member]
Amortized Cost or Cost	317,179
Fair Value	333,961
Carrying Amount	318,137
Held-to-maturity Securities [Member] \| Foreign Government Obligations [Member]
Amortized Cost or Cost	5,292
Fair Value	5,394
Carrying Amount	5,339
Held-to-maturity Securities [Member] \| Obligations of States and Political Subdivisions [Member]
Amortized Cost or Cost	285,301
Fair Value	299,132
Carrying Amount	287,372
Held-to-maturity Securities [Member] \| Public utilities [Member]
Amortized Cost or Cost	11,019
Fair Value	12,483
Carrying Amount	11,000
Held-to-maturity Securities [Member] \| All Other Corporate Securities [Member]
Amortized Cost or Cost	7,880
Fair Value	8,939
Carrying Amount	7,626
Held-to-maturity Securities [Member] \| Asset-backed Securities [Member]
Amortized Cost or Cost	2,818
Fair Value	2,823
Carrying Amount	2,363
Held-to-maturity Securities [Member] \| Commercial Mortgage-backed Securities (CMBS) [Member]
Amortized Cost or Cost	4,869
Fair Value	5,190
Carrying Amount	4,437
AFS Fixed Income Securities [Member]
Amortized Cost or Cost	3,975,786
Fair Value	4,066,122
Carrying Amount	4,066,122
AFS Fixed Income Securities [Member] \| U.S. Government and Government Agencies [Member]
Amortized Cost or Cost	116,666
Fair Value	124,130
Carrying Amount	124,130
AFS Fixed Income Securities [Member] \| Foreign Government Obligations [Member]
Amortized Cost or Cost	27,035
Fair Value	27,831
Carrying Amount	27,831
AFS Fixed Income Securities [Member] \| Obligations of States and Political Subdivisions [Member]
Amortized Cost or Cost	1,208,776
Fair Value	1,246,264
Carrying Amount	1,246,264
AFS Fixed Income Securities [Member] \| Public utilities [Member]
Amortized Cost or Cost	149,006
Fair Value	150,977
Carrying Amount	150,977
AFS Fixed Income Securities [Member] \| All Other Corporate Securities [Member]
Amortized Cost or Cost	1,614,421
Fair Value	1,648,829
Carrying Amount	1,648,829
AFS Fixed Income Securities [Member] \| Asset-backed Securities [Member]
Amortized Cost or Cost	176,837
Fair Value	177,224
Carrying Amount	177,224
AFS Fixed Income Securities [Member] \| Commercial Mortgage-backed Securities (CMBS) [Member]
Amortized Cost or Cost	177,932
Fair Value	179,593
Carrying Amount	179,593
AFS Fixed Income Securities [Member] \| Residential Mortgage Backed Securities (RMBS) [Member]
Amortized Cost or Cost	505,113
Fair Value	511,274
Carrying Amount	511,274
Equity Securities [Member]
Amortized Cost or Cost	159,011
Fair Value	191,400
Carrying Amount	191,400
Equity Securities [Member] \| Public Utility, Equities [Member]
Amortized Cost or Cost	8,815
Fair Value	10,284
Carrying Amount	10,284
Equity Securities [Member] \| Banks, Trust and Insurance Companies [Member]
Amortized Cost or Cost	30,187
Fair Value	35,348
Carrying Amount	35,348
Equity Securities [Member] \| Industrial, Miscellaneous, and All Other [Member]
Amortized Cost or Cost	120,009
Fair Value	145,768
Carrying Amount	145,768
Short-term Investments [Member]
Amortized Cost or Cost	131,972
Fair Value	131,972
Carrying Amount	131,972
Other Investments [Member]
Amortized Cost or Cost	99,203
Carrying Amount	$ 99,203

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 15

-Article 12

Reference 2: 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=34726532&loc=d3e611379-123010

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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.

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