Loans - Investment in Loans by Portfolio Segment and Based on Impairment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	$ 17,221	$ 20,554	$ 17,687	$ 21,116
Provision (recovery) for loan losses	753	(1,614)	569	(1,581)
Charge-offs	(1,464)	(1,192)	(2,176)	(2,356)
Recoveries	371	516	801	1,085
Allowance, Ending balance	16,881	18,264	16,881	18,264
Loans individually evaluated for impairment	3,085	3,625	3,085	3,625	$ 3,310
Loans collectively evaluated for impairment	13,796		13,796		14,377
Loans individually evaluated for impairment	43,854	47,080	43,854	47,080	45,897
Loans collectively evaluated for impairment	1,196,533		1,196,533		1,118,986
Total loans	1,240,387		1,240,387		1,164,883
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	5,945	7,275	5,690	6,984
Provision (recovery) for loan losses	1,015	(1,565)	1,173	(1,075)
Charge-offs	(779)	(509)	(794)	(951)
Recoveries	208	318	320	561
Allowance, Ending balance	6,389	5,519	6,389	5,519
Loans individually evaluated for impairment	673		673		717
Loans collectively evaluated for impairment	5,716		5,716		4,973
Loans individually evaluated for impairment	13,592		13,592		14,845
Loans collectively evaluated for impairment	299,683		299,683		238,066
Total loans	313,275		313,275		252,911
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	7,666	9,337	8,517	9,830
Provision (recovery) for loan losses	(278)	(201)	(1,149)	(531)
Charge-offs	(328)	(236)	(494)	(551)
Recoveries	22	55	208	207
Allowance, Ending balance	7,082	8,955	7,082	8,955
Loans individually evaluated for impairment	1,651		1,651		1,751
Loans collectively evaluated for impairment	5,431		5,431		6,766
Loans individually evaluated for impairment	19,239		19,239		19,209
Loans collectively evaluated for impairment	724,177		724,177		712,009
Total loans	743,416		743,416		731,218
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	3,610	3,942	3,480	4,302
Provision (recovery) for loan losses	16	152	545	25
Charge-offs	(357)	(447)	(888)	(854)
Recoveries	141	143	273	317
Allowance, Ending balance	3,410	$ 3,790	3,410	$ 3,790
Loans individually evaluated for impairment	761		761		842
Loans collectively evaluated for impairment	2,649		2,649		2,638
Loans individually evaluated for impairment	11,023		11,023		11,843
Loans collectively evaluated for impairment	172,673		172,673		168,911
Total loans	$ 183,696		$ 183,696		$ 180,754