Summary of Quarterly Financial Data (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
Quarterly Financial Data [Abstract]
Interest income	$ 264,534	$ 256,554	$ 252,393	$ 249,323	$ 242,814	$ 238,093	$ 233,654	$ 231,401	$ 1,022,803	$ 945,962	$ 928,692
Net interest income	233,530	226,007	221,449	218,193	212,620	207,790	203,644	203,263	899,180	827,318	819,284
Provision for loan losses	6,259	5,671	6,693	9,377	5,021	2,956	6,636	4,397	28,000	19,010	33,831
Income before income taxes	108,068	102,620	94,031	83,730	90,741	93,986	88,034	85,812	388,451	358,573	302,559
Income tax expense	39,519	37,375	33,574	31,199	32,342	36,058	32,242	31,849	141,667	132,491	107,310
Net income	68,549	65,245	60,457	52,531	58,398	57,928	55,792	53,963	246,784	226,082	195,249
Net income available common shareholders	$ 65,990	$ 62,686	$ 57,898	$ 49,972	$ 55,839	$ 55,369	$ 53,233	$ 51,404	$ 236,546	$ 215,844	$ 185,011
Net income per common share, basic (per share)	$ 0.54	$ 0.51	$ 0.46	$ 0.39	$ 0.43	$ 0.42	$ 0.40	$ 0.38	$ 1.90	$ 1.63	$ 1.34
Net income per common share, diluted (per share)	$ 0.54	$ 0.51	$ 0.46	$ 0.39	$ 0.43	$ 0.42	$ 0.40	$ 0.38	$ 1.89	$ 1.62	$ 1.33
Allowance for loan losses and provision for loan losses	$ 12,900								$ 13,300