Securities (Available-for-sale Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,292,998
Amortized Cost, Equity Securities	18,435	$ 17,086
Amortized Cost, Total	3,311,433	2,492,620
Gross Unrealized Gains	29,765	4,662
Gross Unrealized Losses	(28,402)	(46,573)
Securities available for sale	3,294,361
Estimated Fair Value, Equity Securities	18,435	17,086
Estimated Fair Value, Total	3,312,796	2,450,709
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		2,475,534
Gross Unrealized Gains		4,662
Gross Unrealized Losses		(46,573)
Securities available for sale		2,433,623
U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,844	32,075
Gross Unrealized Gains	49	3
Gross Unrealized Losses	0	(127)
Securities available for sale	9,893	31,951
Mortgage and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,579,081	2,061,358
Gross Unrealized Gains	17,200	3,740
Gross Unrealized Losses	(19,003)	(38,400)
Securities available for sale	2,577,278	2,026,698
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	704,073	382,101
Gross Unrealized Gains	12,516	919
Gross Unrealized Losses	(9,399)	(8,046)
Securities available for sale	$ 707,190	$ 374,974

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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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