Shareholders' Equity (Reclassification from Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (losses) on available-for-sale securities, net	$ (79)	$ (98)	$ (24)	$ 524	$ 18	$ (153)	$ (336)	$ (33)	$ 323	$ (504)	$ (3,000)
Income before taxes	56,408	62,197	70,126	63,035	61,802	65,258	63,031	56,340	251,765	246,431	224,440
Income tax expense	(20,896)	(23,842)	(26,295)	(23,983)	(23,669)	(25,034)	(24,490)	(21,840)	(95,016)	(95,033)	(87,230)
Net income	$ 35,512	$ 38,355	$ 43,831	$ 39,052	$ 38,133	$ 40,224	$ 38,541	$ 34,500	156,749	151,398	137,210
Interest on deposits									48,863	48,411	53,191
Interest on junior subordinated debentures									8,230	8,079	$ 11,369
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated unrealized losses on securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (losses) on available-for-sale securities, net									323	(504)
Income before taxes									323	(504)
Income tax expense									(127)	200
Net income									196	(304)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated unrealized losses on derivative instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before taxes									(2,082)	(1,974)
Income tax expense									817	785
Net income									(1,265)	(1,189)
Interest on deposits									252	0
Interest on junior subordinated debentures									$ 1,830	$ 1,974