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Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands | Jun. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | $ 5,571,491 | $ 5,270,798
Unrealized Gains | 195,287 | 47,369
Unrealized Losses | (8,880) | (45,067)
Debt Securities, Available-for-sale | 5,757,898 | 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 | 143,461 | 120,092
Unrealized Gains | 3,683 | 1,810
Unrealized Losses | (20) | (592)
Debt Securities, Available-for-sale | 147,124 | 121,310
AFS Fixed Income Securities [Member] | Foreign Government [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 20,995 | 23,202
Unrealized Gains | 494 | 36
Unrealized Losses | 0 | (107)
Debt Securities, Available-for-sale | 21,489 | 23,131
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 1,056,507 | 1,121,615
Unrealized Gains | 54,516 | 19,485
Unrealized Losses | (6) | (2,631)
Debt Securities, Available-for-sale | 1,111,017 | 1,138,469
AFS Fixed Income Securities [Member] | Corporate Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 1,733,319 | 1,639,852
Unrealized Gains | 64,620 | 5,521
Unrealized Losses | (4,402) | (27,965)
Debt Securities, Available-for-sale | 1,793,537 | 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 | 762,896 | 720,193
Unrealized Gains | 8,649 | 4,112
Unrealized Losses | (3,941) | (6,943)
Debt Securities, Available-for-sale | 767,604 | 717,362
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 541,093 | 527,409
Unrealized Gains | 24,737 | 3,417
Unrealized Losses | (237) | (3,748)
Debt Securities, Available-for-sale | 565,593 | 527,078
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost/Amortized Cost | 1,313,220 | 1,118,435
Unrealized Gains | 38,588 | 12,988
Unrealized Losses | (274) | (3,081)
Debt Securities, Available-for-sale | $ 1,351,534 | $ 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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