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Securities (Securities Available for Sale) (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 3,703,096	$ 3,210,615
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		63,486	12,799
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(20,440)	(55,966)
Securities available for sale		3,746,142	3,167,448
Debt Securities, Available-for-sale, Amortized Cost		3,703,096
Debt Securities, Available-for-sale		3,746,142	3,167,448
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	2,864,949	2,045,728
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	[1]	47,223	8,473
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	[1]	(19,222)	(40,846)
Securities available for sale	[1]	2,892,950	2,013,355
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	[1]	194,563	176,793
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	[1]	2,476	763
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	[1]	(989)	(2,621)
Debt Securities, Available-for-sale	[1]	196,050	174,935
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		478,366	579,755
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		10,660	2,328
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(224)	(7,760)
Securities available for sale		488,802	574,323
U.S. Government Agency and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		165,218	408,088
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		3,127	1,235
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(5)	(4,736)
Securities available for sale		$ 168,340	404,587
US Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost			251
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax			0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax			(3)
Securities available for sale			$ 248
[1] Beginning in 2019, other asset-backed securities were presented separately in this table. Prior period amounts that were previously reported in U.S. government agency and government-sponsored enterprise mortgage-backed securities and collateralized mortgage obligations have been reclassified to conform to current period presentation.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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