Quarterly Results of Operations - Summary of Quarterly Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 43,492	$ 42,311	$ 42,517	$ 43,087	$ 46,280	$ 45,492	$ 46,005	$ 46,885	$ 47,377	$ 49,522	$ 48,478	$ 50,098	$ 171,407	$ 184,662	$ 195,475
Interest expense	3,563	3,629	3,662	3,608	3,696	3,597	3,582	3,538	3,787	4,007	4,191	4,529	14,462	14,413	16,514
Net interest income before provision for loan losses	39,929	38,682	38,855	39,479	42,584	41,895	42,423	43,347	43,590	45,515	44,287	45,569	156,945	170,249	178,961
Provision for loan losses	5,423	3,710	1,858	1,453	1,265	1,515	1,660	1,769	772	437	1,670	1,417	12,444	6,209	4,296
Net interest income after provision for loan losses	34,506	34,972	36,997	38,026	41,319	40,380	40,763	41,578	42,818	45,078	42,617	44,152	144,501	164,040	174,665
Non-interest income	15,419	3,761	2,747	(479)	(5,117)	1,614	2,161	(354)	2,364	3,338	7,324	7,151	21,448	(1,696)	20,177
Non-interest expense	42,230	38,677	40,393	36,724	33,149	37,981	39,855	39,018	44,238	46,613	45,230	47,884	158,024	150,003	183,965
Income before income taxes	7,695	56	(649)	823	3,053	4,013	3,069	2,206	944	1,803	4,711	3,419	7,925	12,341	10,877
Income tax (benefit) expense	4,355	(1,580)	692	(423)	774	676	940	775	(56)	856	1,813	1,337	3,044	3,165	3,950
Net income	$ 3,340	$ 1,636	$ (1,341)	$ 1,246	$ 2,279	$ 3,337	$ 2,129	$ 1,431	$ 1,000	$ 947	$ 2,898	$ 2,082	$ 4,881	$ 9,176	$ 6,927
Income per share-basic (in dollars per share)	$ 0.11	$ 0.05	$ (0.04)	$ 0.03	$ 0.06	$ 0.08	$ 0.05	$ 0.03	$ 0.02	$ 0.02	$ 0.06	$ 0.04	$ 0.14	$ 0.22	$ 0.14
Income per share-diluted (in dollars per share)	$ 0.11	$ 0.05	$ (0.04)	$ 0.03	$ 0.06	$ 0.08	$ 0.05	$ 0.03	$ 0.02	$ 0.02	$ 0.06	$ 0.04	$ 0.14	$ 0.22	$ 0.14