Selected Quarterly Consolidated Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Selected Quarterly Financial Information [Abstract]
Interest income	$ 211,432	$ 205,715	$ 202,431	$ 202,335	$ 198,160	$ 191,998	$ 186,970	$ 182,912	$ 821,913	$ 760,040	$ 718,941
Interest expense	26,173	25,518	25,526	26,183	24,820	23,988	23,459	23,148	103,400	95,415	90,500
Net interest income	185,259	180,197	176,905	176,152	173,340	168,010	163,511	159,764	718,513	664,625	628,441
Provision for loan and lease losses	12,500	14,250	14,000	15,600	13,800	13,000	12,750	9,750	56,350	49,300	37,250
Non-interest income	70,617	66,412	65,075	62,374	59,679	61,292	59,245	57,561
Non-interest expense	161,871	156,097	152,778	152,445	143,780	139,937	137,537	134,087	623,191	555,341	501,600
Income before income tax expense	81,505	76,262	75,202	70,481	75,439	76,365	72,469	73,488	303,450	297,761	291,699
Income tax expense	23,845	24,445	24,599	23,434	23,627	24,995	20,426	23,984	96,323	93,032	91,973
Net income	57,660	51,817	50,603	47,047	51,812	51,370	52,043	49,504	207,127	204,729	199,726
Earnings applicable to common shareholders	$ 55,501	$ 49,634	$ 48,398	$ 44,921	$ 49,646	$ 49,176	$ 49,819	$ 46,719	$ 199,031	$ 196,018	$ 189,170
Earnings per common share:
Earnings per common share, Basic (in dollars per share)	$ 0.61	$ 0.54	$ 0.53	$ 0.49	$ 0.54	$ 0.54	$ 0.55	$ 0.52	$ 2.17	$ 2.15	$ 2.10
Earnings per common share, Diluted (in dollars per share)	$ 0.60	$ 0.54	$ 0.53	$ 0.49	$ 0.54	$ 0.53	$ 0.55	$ 0.51	$ 2.16	$ 2.13	$ 2.08