Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of the unaudited quarterly results of operations
Interest income	$ 104,587	$ 100,695	$ 87,579	$ 81,889	$ 85,840	$ 83,032	$ 84,008	$ 76,259	$ 374,750	$ 329,138	$ 263,023
Interest expense	11,325	10,678	7,976	7,874	7,791	7,301	6,851	6,205	37,853	28,147	21,665
Net interest income	93,262	90,017	79,603	74,015	78,049	75,731	77,157	70,054	336,897	300,991	241,358
Provision for loan losses	2,150	2,150	1,750	1,500	1,650	2,650	1,430	1,800	7,550	7,530	4,750
Noninterest income	32,441	33,413	34,265	32,021	30,255	38,272	35,586	33,302	132,140	137,415	108,270
Noninterest expense	76,808	80,660	74,841	69,309	71,558	76,468	77,259	69,814	301,618	295,099	245,114
Income before income taxes	46,745	40,620	37,277	35,227	35,096	34,885	34,054	31,742	159,869	135,777	99,764
Income taxes	30,234	14,199	11,993	11,255	11,461	11,706	11,154	10,526	67,681	44,847	31,750
Net income	$ 16,511	$ 26,421	$ 25,284	$ 23,972	$ 23,635	$ 23,179	$ 22,900	$ 21,216	$ 92,188	$ 90,930	$ 68,014
Basic earnings per share (usd per share)	$ 0.33	$ 0.54	$ 0.57	$ 0.54	$ 0.56	$ 0.55	$ 0.54	$ 0.53	$ 1.97	$ 2.18	$ 1.89
Diluted earnings per share (usd per share)	$ 0.33	$ 0.53	$ 0.57	$ 0.54	$ 0.55	$ 0.55	$ 0.54	$ 0.52	$ 1.96	$ 2.17	$ 1.88