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Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | $ 5,706,656 | $ 5,270,798
Unrealized Gains | 231,328 | 47,369
Unrealized Losses | (7,747) | (45,067)
Debt Securities, Available-for-sale | 5,930,237 | 5,273,100
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 116,555 | 120,092
Unrealized Gains | 4,357 | 1,810
Unrealized Losses | (12) | (592)
Debt Securities, Available-for-sale | 120,900 | 121,310
AFS Fixed Income Securities [Member] | Foreign Government [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 20,947 | 23,202
Unrealized Gains | 573 | 36
Unrealized Losses | 0 | (107)
Debt Securities, Available-for-sale | 21,520 | 23,131
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 1,127,709 | 1,121,615
Unrealized Gains | 62,910 | 19,485
Unrealized Losses | (4) | (2,631)
Debt Securities, Available-for-sale | 1,190,615 | 1,138,469
AFS Fixed Income Securities [Member] | Corporate Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 1,762,981 | 1,639,852
Unrealized Gains | 78,345 | 5,521
Unrealized Losses | (2,399) | (27,965)
Debt Securities, Available-for-sale | 1,838,927 | 1,617,408
AFS Fixed Income Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 764,038 | 720,193
Unrealized Gains | 8,998 | 4,112
Unrealized Losses | (4,653) | (6,943)
Debt Securities, Available-for-sale | 768,383 | 717,362
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 524,441 | 527,409
Unrealized Gains | 31,435 | 3,417
Unrealized Losses | (145) | (3,748)
Debt Securities, Available-for-sale | 555,731 | 527,078
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 1,389,985 | 1,118,435
Unrealized Gains | 44,710 | 12,988
Unrealized Losses | (534) | (3,081)
Debt Securities, Available-for-sale | $ 1,434,161 | $ 1,128,342

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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