Quarterly Financial Data - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 42,417	$ 42,172	$ 40,030	$ 38,396	$ 38,056	$ 36,705	$ 26,112	$ 25,734	$ 163,015	$ 126,607	$ 101,983
Interest expense	5,711	5,285	4,730	4,113	3,884	3,836	2,451	2,211	19,839	12,382	8,065
Net interest income	36,706	36,887	35,300	34,283	34,172	32,869	23,661	23,523	143,176	114,225	93,918
Provision for loan and lease losses	1,992	2,689	2,766	2,445	2,250	1,415	830	326	9,892	4,821	3,802
Net interest income after provision for loan and lease losses	34,714	34,198	32,534	31,838	31,922	31,454	22,831	23,197	133,284	109,404	90,116
Noninterest income	14,152	14,109	16,009	14,970	13,994	14,137	14,001	13,831	59,240	55,963	52,425
Total noninterest expense	33,440	32,695	32,548	32,030	38,430	47,066	29,546	26,939	130,713	141,981	105,515
Income before income taxes	15,426	15,612	15,995	14,778	7,486	(1,475)	7,286	10,089	61,811	23,386	37,026
Income taxes	5,162	4,416	4,217	3,922	568	(1,533)	2,046	2,800	17,717	3,881	9,758
Net income	$ 10,264	$ 11,196	$ 11,778	$ 10,856	$ 6,918	$ 58	$ 5,240	$ 7,289	$ 44,094	$ 19,505	$ 27,268
Weighted average shares outstanding - basic earnings per share	27,254	26,437	26,380	26,345	26,300	26,273	19,434	19,402	26,606	22,871	19,491
Weighted average shares outstanding - diluted earnings per share	27,356	26,542	26,477	26,448	26,436	26,340	19,469	19,433	26,708	22,931	19,522
Net income per share:
Basic (in dollars per share)	$ 0.37	$ 0.42	$ 0.44	$ 0.41	$ 0.27	$ 0.00	$ 0.27	$ 0.37	$ 1.64	$ 0.85	$ 1.39
Diluted (in dollars per share)	0.37	0.42	0.44	0.41	0.27	0.00	0.27	0.37	1.64	0.84	1.39
Dividends per share	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.80	$ 0.80	$ 0.80