Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 137,105	$ 117,795	$ 106,574	$ 100,380	$ 104,587	$ 100,695	$ 87,579	$ 81,889	$ 461,854	$ 374,750	$ 329,138
Interest expense	21,648	18,356	14,185	11,140	11,325	10,678	7,976	7,874	65,329	37,853	28,147
Net interest income	115,457	99,439	92,389	89,240	93,262	90,017	79,603	74,015	396,525	336,897	300,991
Provision for loan losses	1,000	2,250	1,810	1,750	2,150	2,150	1,750	1,500	6,810	7,550	7,530
Noninterest income	36,374	38,053	35,581	33,953	32,441	33,413	34,265	32,021	143,961	132,140	137,415
Noninterest expense	93,313	94,746	79,026	77,944	76,808	80,660	74,841	69,309	345,029	301,618	295,099
Income before income taxes	57,518	40,496	47,134	43,499	46,745	40,620	37,277	35,227	188,647	159,869	135,777
Income taxes	13,098	8,532	10,424	9,673	30,234	14,199	11,993	11,255	41,727	67,681	44,847
Net income	$ 44,420	$ 31,964	$ 36,710	$ 33,826	$ 16,511	$ 26,421	$ 25,284	$ 23,972	$ 146,920	$ 92,188	$ 90,930
Basic earnings per share (usd per share)	$ 0.76	$ 0.61	$ 0.74	$ 0.69	$ 0.33	$ 0.54	$ 0.57	$ 0.54	$ 2.80	$ 1.97	$ 2.18
Diluted earnings per share (usd per share)	$ 0.76	$ 0.61	$ 0.74	$ 0.68	$ 0.33	$ 0.53	$ 0.57	$ 0.54	$ 2.79	$ 1.96	$ 2.17