Unaudited Interim Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Unaudited Interim Financial Data
Total interest income	$ 88,796	$ 91,691	$ 91,466	$ 84,281	$ 74,314	$ 72,761	$ 70,325	$ 68,633	$ 356,234	$ 286,033	$ 224,302
Total interest expense	16,860	18,215	18,038	15,898	13,811	11,987	9,953	8,876	69,011	44,627	20,936
Net interest income	71,936	73,476	73,428	68,383	60,503	60,774	60,372	59,757	287,223	241,406	203,366
Provision for loan losses	2,367	3,411	2,517	2,111	405	758	2,258	1,008	10,406	4,429	5,303
Total non-interest income	31,638	30,936	27,896	25,945	22,852	21,853	22,802	22,486	116,415	89,993	84,474
Total non-interest expense	65,490	68,121	68,020	57,163	48,769	45,929	47,305	51,040	258,794	193,043	174,426
Income before income taxes	35,717	32,880	30,787	35,054	34,181	35,940	33,611	30,195	134,438	133,927	108,111
Income taxes	7,146	8,052	6,702	9,585	8,891	9,081	8,749	8,278	31,485	34,999	45,385
Net income	$ 28,571	$ 24,828	$ 24,085	$ 25,469	$ 25,290	$ 26,859	$ 24,862	$ 21,917	$ 102,953	$ 98,928	$ 62,726
Basic earnings per share (in dollars per share)	$ 0.52	$ 0.45	$ 0.43	$ 0.48	$ 0.52	$ 0.55	$ 0.51	$ 0.45	$ 1.88	$ 2.02	$ 1.47
Diluted earnings per share (in dollars per share)	$ 0.52	$ 0.45	$ 0.43	$ 0.48	$ 0.51	$ 0.55	$ 0.51	$ 0.45	$ 1.87	$ 2.01	$ 1.45