Shareholders' Equity (Reclassification from Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on investment securities, net	$ 587	$ 710	$ 864	$ 1,364	$ (2,649)	$ 90	$ 12	$ (351)	$ 3,525	$ (2,898)	$ 45
Interest on deposits									278,892	166,553	83,326
Interest on junior subordinated debentures									12,001	11,222	9,782
Income before taxes	116,682	134,601	110,173	118,645	107,662	122,814	121,591	108,066	480,101	460,133	389,997
Income tax expense	(30,718)	(35,480)	(28,707)	(29,499)	(28,005)	(30,866)	(32,011)	(26,085)	(124,404)	(116,967)	(132,315)
Net income	$ 85,964	$ 99,121	$ 81,466	$ 89,146	$ 79,657	$ 91,948	$ 89,580	$ 81,981	355,697	343,166	$ 257,682
Reclassification out of Accumulated Other Comprehensive Income | Accumulated unrealized gains on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains on investment securities, net									899	33
Income before taxes									899	33
Income tax expense									(241)	(9)
Net income									658	24
Reclassification out of Accumulated Other Comprehensive Income | Accumulated unrealized losses on derivative instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest on deposits									(10,954)	(7,549)
Interest on other borrowings									576	236
Interest on junior subordinated debentures									128	0
Income before taxes									10,250	7,313
Income tax expense									(2,733)	(1,965)
Net income									$ 7,517	$ 5,348