Investments (Available-For-Sale Securities Disclosure) (Details) - Available-for-sale Securities [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	$ 5,879,986	$ 5,270,798
Unrealized Gains	223,372	47,369
Unrealized Losses	(7,738)	(45,067)
Total AFS securities	6,095,620	5,273,100
U.S. Government and Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	112,680	120,092
Unrealized Gains	3,506	1,810
Unrealized Losses	0	(592)
Total AFS securities	116,186	121,310
Foreign Government [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	18,011	23,202
Unrealized Gains	533	36
Unrealized Losses	(2)	(107)
Total AFS securities	18,542	23,131
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,168,185	1,121,615
Unrealized Gains	62,175	19,485
Unrealized Losses	(270)	(2,631)
Total AFS securities	1,230,090	1,138,469
Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,866,881	1,639,852
Unrealized Gains	81,906	5,521
Unrealized Losses	(1,310)	(27,965)
Total AFS securities	1,947,477	1,617,408
Collateralized Loan Obligations and Other Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	790,517	720,193
Unrealized Gains	7,929	4,112
Unrealized Losses	(5,434)	(6,943)
Total AFS securities	793,012	717,362
Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	514,709	527,409
Unrealized Gains	23,902	3,417
Unrealized Losses	(267)	(3,748)
Total AFS securities	538,344	527,078
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,409,003	1,118,435
Unrealized Gains	43,421	12,988
Unrealized Losses	(455)	(3,081)
Total AFS securities	$ 1,451,969	$ 1,128,342

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

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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=118939692&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ 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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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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