Summary of Quarterly Statements of Income (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	$ 144,416	$ 103,562	$ 82,937	$ 79,464	$ 80,629	$ 78,851	$ 69,679	$ 62,630	$ 410,379	$ 291,789	$ 227,261
Interest expense	11,969	6,753	5,442	5,134	5,153	5,234	3,944	3,450	29,298	17,781	14,710
Net Interest Income	132,447	96,809	77,495	74,330	75,476	73,617	65,735	59,180	381,081	274,008	212,551
Provision for loan losses	6,272	4,103	3,000	1,500	2,000	1,500	1,500	1,500	14,875	6,500	6,100
Noninterest income	54,264	27,770	20,897	19,419	20,052	20,215	20,674	19,275	122,350	80,216	63,095
Operating expenses	114,302	106,144	59,085	58,887	57,824	58,265	56,785	51,020	338,418	223,894	179,925
Income before income taxes	66,137	14,332	36,307	33,362	35,704	34,067	28,124	25,935	150,138	123,830	89,621
Income tax expense	18,969	2,848	10,532	9,757	10,200	9,600	9,100	8,100	42,106	37,000	27,500
Net income	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	$ 108,032	$ 86,830	$ 62,121
Basic earnings per common share (usd per share)	$ 0.67	$ 0.23	$ 0.67	$ 0.61	$ 0.67	$ 0.64	$ 0.54	$ 0.54	$ 2.21	$ 2.41	$ 1.98
Diluted earnings per common share (usd per share)	0.66	0.23	0.67	0.60	0.66	0.64	0.54	0.54	2.17	2.39	1.97
Cash dividends declared per share (in dollars per share)	$ 0.27	$ 0.27	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.24	$ 0.24	$ 1.06	$ 1.00	$ 0.94