Quarterly Financial Data (unaudited) - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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	$ 51,239	$ 49,255	$ 46,460	$ 43,534	$ 42,417	$ 42,172	$ 40,030	$ 38,396	$ 190,488		$ 163,015		$ 126,607
Interest expense	9,862	8,832	7,470	6,262	5,711	5,285	4,730	4,113	32,426		19,839		12,382
Net interest income	41,377	40,423	38,990	37,272	36,706	36,887	35,300	34,283	158,062	[1]	143,176	[1]	114,225	[1]
Provision for loan and lease losses	103	2,745	15,409	2,053	1,992	2,689	2,766	2,445	20,310		9,892		4,821
Net interest income after provision for loan and lease losses	41,274	37,678	23,581	35,219	34,714	34,198	32,534	31,838	137,752		133,284		109,404
Noninterest income	14,416	14,861	15,314	15,582	14,152	14,109	16,009	14,970	60,173		59,240		55,963
Total noninterest expense	33,396	34,371	34,347	35,125	33,440	32,695	32,548	32,030	137,239		130,713		141,981
Income before income taxes	22,294	18,168	4,548	15,676	15,426	15,612	15,995	14,778	60,686		61,811		23,386
Income taxes	3,922	3,204	191	2,826	5,162	4,416	4,217	3,922	10,143		17,717		3,881
Net income	$ 18,372	$ 14,964	$ 4,357	$ 12,850	$ 10,264	$ 11,196	$ 11,778	$ 10,856	$ 50,543		$ 44,094		$ 19,505
Weighted average shares outstanding - basic earnings per share	29,161	29,232	29,176	29,140	27,254	26,437	26,380	26,345	29,177		26,606		22,871
Weighted average shares outstanding - diluted earnings per share	29,220	29,318	29,271	29,234	27,356	26,542	26,477	26,448	29,259		26,708		22,931
Net income per share:
Basic (in dollars per share)	$ 0.63	$ 0.51	$ 0.15	$ 0.44	$ 0.37	$ 0.42	$ 0.44	$ 0.41	$ 1.72		$ 1.64		$ 0.85
Diluted (in dollars per share)	0.63	0.51	0.15	0.44	0.37	0.42	0.44	0.41	1.72		1.64		0.84
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

[1] (1)Net interest income as well as many other revenues for financial assets and liabilities including loans, leases, securities, and derivatives are excluded from the scope of the standard. Noninterest income streams that are out-of-scope of the standard include bank owned life insurance income, sales of investment securities and mortgage banking activities.