Shareholders' Equity (Reclassification from Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (losses) on investment securities, net									$ 7,645	$ 323	$ (504)
Interest on deposits									58,409	48,863	48,411
Interest on junior subordinated debentures									9,503	8,230	8,079
Income before taxes	$ 88,332	$ 85,054	$ 79,971	$ 78,497	$ 56,408	$ 62,197	$ 70,126	$ 63,035	331,854	251,765	246,431
Income tax expense	(33,724)	(31,939)	(29,930)	(29,386)	(20,896)	(23,842)	(26,295)	(23,983)	(124,979)	(95,016)	(95,033)
Net income	$ 54,608	$ 53,115	$ 50,041	$ 49,111	$ 35,512	$ 38,355	$ 43,831	$ 39,052	206,875	156,749	$ 151,398
Reclassification out of Accumulated Other Comprehensive Income | Accumulated unrealized losses on securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (losses) on investment securities, net									7,645	323
Income before taxes									7,645	323
Income tax expense									(3,004)	(127)
Net income									4,641	196
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									1,345	252
Interest on junior subordinated debentures									1,775	1,830
Income before taxes									(3,120)	(2,082)
Income tax expense									1,226	817
Net income									$ (1,894)	$ (1,265)