Loans Receivable, Net - Allowance for Loan Losses and Recorded Investment in Loans by Portfolio Segment and Based on Impairment Method (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Allowance for loan losses:
Balance at beginning of period	$ 20,494	$ 18,241	$ 20,510	$ 18,230
Provision (benefit) charged to operations	800	1,700	1,900	3,400
Charge-offs	(938)	(2,542)	(2,299)	(4,342)
Recoveries	464	258	709	369
Balance at end of period	20,820	17,657	20,820	17,657
Ending allowance balance attributed to loans:
Individually evaluated for impairment	3,436		3,436		2,554
Collectively evaluated for impairment	17,384		17,384		17,956
Total ending allowance balance	20,820		20,820		20,510
Loans:
Loans individually evaluated for impairment	37,099		37,099		37,546
Loans collectively evaluated for impairment	1,489,487		1,489,487		1,505,691
Total ending loan balance	1,526,586		1,526,586		1,543,237
Residential Real Estate [Member]
Allowance for loan losses:
Balance at beginning of period	5,185	4,164	5,241	5,370
Provision (benefit) charged to operations	19	1,961	849	2,101
Charge-offs	(739)	(1,529)	(1,689)	(2,904)
Recoveries	435	172	499	201
Balance at end of period	4,900	4,768	4,900	4,768
Ending allowance balance attributed to loans:
Individually evaluated for impairment	194		194		179
Collectively evaluated for impairment	4,706		4,706		5,062
Total ending allowance balance	4,900		4,900		5,241
Loans:
Loans individually evaluated for impairment	21,000		21,000		22,427
Loans collectively evaluated for impairment	768,737		768,737		789,545
Total ending loan balance	789,737		789,737		811,972
Commercial Real Estate [Member]
Allowance for loan losses:
Balance at beginning of period	9,286	8,609	8,937	8,474
Provision (benefit) charged to operations	463	(76)	787	32
Charge-offs				(47)
Recoveries	25	81	50	155
Balance at end of period	9,774	8,614	9,774	8,614
Ending allowance balance attributed to loans:
Individually evaluated for impairment	2,757		2,757		1,834
Collectively evaluated for impairment	7,705		7,705		7,103
Total ending allowance balance	10,462		10,462		8,937
Loans:
Loans individually evaluated for impairment	12,375		12,375		12,116
Loans collectively evaluated for impairment	465,225		465,225		463,039
Total ending loan balance	477,600		477,600		475,155
Consumer [Member]
Allowance for loan losses:
Balance at beginning of period	2,148	1,861	2,264	1,461
Provision (benefit) charged to operations	(13)	798	(107)	1,570
Charge-offs	(199)	(1,013)	(375)	(1,391)
Recoveries	3	2	157	8
Balance at end of period	1,939	1,648	1,939	1,648
Ending allowance balance attributed to loans:
Individually evaluated for impairment	485		485		541
Collectively evaluated for impairment	1,454		1,454		1,723
Total ending allowance balance	1,939		1,939		2,264
Loans:
Loans individually evaluated for impairment	3,440		3,440		2,712
Loans collectively evaluated for impairment	188,885		188,885		195,431
Total ending loan balance	192,325		192,325		198,143
Commercial [Member]
Allowance for loan losses:
Balance at beginning of period	1,094	1,225	1,348	900
Provision (benefit) charged to operations	(2)	(118)	(23)	205
Charge-offs			(235)
Recoveries	1	3	3	5
Balance at end of period	1,093	1,110	1,093	1,110
Ending allowance balance attributed to loans:
Collectively evaluated for impairment	406		406		1,348
Total ending allowance balance	406		406		1,348
Loans:
Loans individually evaluated for impairment	284		284		291
Loans collectively evaluated for impairment	66,640		66,640		57,676
Total ending loan balance	66,924		66,924		57,967
Unallocated [Member]
Allowance for loan losses:
Balance at beginning of period	2,781	2,382	2,720	2,025
Provision (benefit) charged to operations	333	(865)	394	(508)
Balance at end of period	3,114	1,517	3,114	1,517
Ending allowance balance attributed to loans:
Collectively evaluated for impairment	3,113		3,113		2,720
Total ending allowance balance	$ 3,113		$ 3,113		$ 2,720