Selected Quarterly Financial Data (Unaudited) (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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Total interest income	$ 71,026	$ 64,438	$ 62,732	$ 62,887	$ 61,785	$ 57,695	$ 55,019	$ 51,791	$ 49,169	$ 47,820	$ 46,850	$ 45,428	$ 44,129	$ 261,083	$ 226,290	$ 184,226
Total interest expense	23,598	22,722	21,889	20,503	18,410	17,112	14,004	12,730	12,240	11,860	11,211	10,651	10,724	88,712	62,256	44,446
Net interest income	47,428	41,716	40,843	42,384	43,375	40,583	41,015	39,061	36,929	35,960	35,639	34,777	33,405	172,371	164,034	139,780
Provision for loan losses	2,519	1,157	112	436	777	1,500	2,400	2,000	3,400	5,676	375	375	0	4,224	6,677	6,426
Net interest income after provision for loan losses	44,909	40,559	40,731	41,948	42,598	39,083	38,615	37,061	33,529	30,284	35,264	34,402	33,405	168,147	157,357	133,354
Total non-interest income	8,709	10,115	6,775	6,037	6,405	5,290	5,450	4,543	4,733	1,630	4,645	5,806	5,534	31,636	21,688	17,172
Total non-interest expense	36,237	31,064	31,841	29,559	31,013	26,590	61,768	26,015	25,601	30,206	24,703	24,903	24,078	128,701	145,386	103,446
Income before income tax expense	17,381	19,610	15,665	18,426	17,990	17,783	(17,703)	15,589	12,661	1,708	15,206	15,305	14,861	71,082	33,659	47,080
Income tax expense	3,832	5,392	3,634	3,507	3,123	6,956	(2,961)	3,805	8,983	194	5,934	5,012	4,868	16,365	10,923	16,008
Net income	$ 13,549	$ 14,218	$ 12,031	$ 14,919	$ 14,867	$ 10,827	$ (14,742)	$ 11,784	$ 3,678	$ 1,514	$ 9,272	$ 10,293	$ 9,993	$ 54,717	$ 22,736	$ 31,072
Earnings per share - basic and diluted (in dollars per share)	$ 0.12	$ 0.13	$ 0.11	$ 0.13	$ 0.13	$ 0.10	$ (0.13)							$ 0.49	$ 0.20
Weighted average shares outstanding - basic and diluted (in shares)	109,958,999	111,371,754	111,553,203	111,536,577	111,423,361	111,389,951	111,360,278							111,101,246	111,395,723