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Investments (Available-For-Sale Securities) (Details) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
U.S. Treasury obligations [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | $ 122,855 | $ 163,714
Gross Unrealized Gains | 1,696 | 3,785
Gross Unrealized Losses | 659 | 987
Estimated Fair Value | 123,892 | 166,512
U.S. Government-sponsored enterprise obligations [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 25,456 | 38,022
Gross Unrealized Gains | 927 | 1,641
Gross Unrealized Losses | 49 | 100
Estimated Fair Value | 26,334 | 39,563
State and municipal bonds [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 904,719 | 1,015,555
Gross Unrealized Gains | 36,739 | 47,395
Gross Unrealized Losses | 823 | 335
Estimated Fair Value | 940,635 | 1,062,615
Corporate debt [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 1,296,128 | 1,389,970
Gross Unrealized Gains | 24,720 | 44,234
Gross Unrealized Losses | 29,162 | 17,103
Estimated Fair Value | 1,291,686 | 1,417,101
Residential mortgage-backed securities [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 233,659 | 266,306
Gross Unrealized Gains | 6,039 | 10,198
Gross Unrealized Losses | 1,311 | 448
Estimated Fair Value | 238,387 | 276,056
Agency commercial mortgage-backed securities [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 10,851 | 15,344
Gross Unrealized Gains | 174 | 208
Gross Unrealized Losses | 26 | 59
Estimated Fair Value | 10,999 | 15,493
Other commercial mortgage-backed securities [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 29,983 | 50,025
Gross Unrealized Gains | 354 | 1,137
Gross Unrealized Losses | 203 | 99
Estimated Fair Value | 30,134 | 51,063
Other asset-backed securities [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 98,412 | 116,541
Gross Unrealized Gains | 54 | 288
Gross Unrealized Losses | 246 | 205
Estimated Fair Value | 98,220 | 116,624
Debt Securities [Member] |  |
Fixed maturities, available for sale |  |
Amortized Cost | 2,722,063 | 3,055,477
Gross Unrealized Gains | 70,703 | 108,886
Gross Unrealized Losses | 32,479 | 19,336
Estimated Fair Value | $ 2,760,287 | $ 3,145,027

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562 + Details
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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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