Quarterly Condensed Financial Information (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
Condensed Financial Statements, Captions [Line Items]
Interest income	$ 54,789	$ 52,468	$ 51,542	$ 43,740	$ 39,438	$ 37,293	$ 37,033	$ 35,460	$ 202,539	$ 149,224	$ 132,779
Interest expense	7,385	6,843	5,909	5,098	3,984	3,463	3,250	3,032	25,235	13,729	12,369
Net interest income	47,404	45,625	45,633	38,642	35,454	33,830	33,783	32,428	177,304	135,495	120,410
Provision for portfolio loan losses	3,186	2,422	3,623	1,533	964	3,038	716	833	10,764	5,551	4,872
Provision reversal for purchased credit impaired loan losses	(279)	0	(207)	(148)	(343)	(1,194)	(336)	(73)	(634)	(1,946)	(4,414)
Net interest income after provision for loan losses	44,497	43,203	42,217	37,257	34,833	31,986	33,403	31,668	167,174	131,890	119,952
Noninterest income	11,112	8,372	7,934	6,976	9,029	6,976	7,049	6,005	34,394	29,059	20,675
Noninterest expense	28,260	27,404	32,651	26,736	23,181	20,814	21,353	20,762	115,051	86,110	82,226
Income before income tax expense	27,349	24,171	17,500	17,497	20,681	18,148	19,099	16,911	86,517	74,839	58,401
Income tax expense	19,820	7,856	5,545	5,106	7,053	6,316	6,747	5,886	38,327	26,002	19,951
Net income	$ 7,529	$ 16,315	$ 11,955	$ 12,391	$ 13,628	$ 11,832	$ 12,352	$ 11,025	$ 48,190	$ 48,837	$ 38,450
Earnings per common share:
Basic (usd per share)	$ 0.33	$ 0.70	$ 0.51	$ 0.57	$ 0.68	$ 0.59	$ 0.62	$ 0.55	$ 2.10	$ 2.44	$ 1.92
Diluted (usd per share)	$ 0.32	$ 0.69	$ 0.50	$ 0.56	$ 0.67	$ 0.59	$ 0.61	$ 0.54	$ 2.07	$ 2.41	$ 1.89