Loans Receivable and Allowance for Loan Losses - Schedule of Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	$ 30,932	$ 23,998
Charge-offs	(1,144)	(536)
Recoveries	143	341
Provision for loan losses	3,635	2,901
Ending balance	33,566	26,704
Loans:
Individually evaluated for impairment	30,503		40,325
Collectively evaluated for impairment	4,254,426		4,214,719
Loans acquired with credit deterioration	52,174		56,617
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	4,337,103		4,311,661
Allowance for loan losses:
Individually evaluated for impairment	3,369		1,342
Collectively evaluated for impairment	23,371		22,575
Loans acquired with credit deterioration	6,826		7,015
Total Allowance for loan losses	33,566	26,704
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	4,746	2,674
Charge-offs	(21)	0
Recoveries	45	90
Provision for loan losses	1,977	(281)
Ending balance	6,747	2,483
Loans:
Individually evaluated for impairment	13,400		15,658
Collectively evaluated for impairment	592,323		524,335
Loans acquired with credit deterioration	2,114		2,672
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	607,837		542,665
Allowance for loan losses:
Individually evaluated for impairment	2,295		818
Collectively evaluated for impairment	4,294		3,766
Loans acquired with credit deterioration	158		162
Total Allowance for loan losses	6,747	2,483
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	13,572	11,478
Charge-offs	(318)	(248)
Recoveries	0	25
Provision for loan losses	1,067	1,377
Ending balance	14,321	12,632
Loans:
Individually evaluated for impairment	12,905		20,387
Collectively evaluated for impairment	1,149,368		1,096,681
Loans acquired with credit deterioration	31,799		32,589
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	1,194,072		1,149,657
Allowance for loan losses:
Individually evaluated for impairment	864		304
Collectively evaluated for impairment	8,645		8,336
Loans acquired with credit deterioration	4,812		4,932
Total Allowance for loan losses	14,321	12,632
Multi-family
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	8,493	4,227
Charge-offs	0	0
Recoveries	0	0
Provision for loan losses	(297)	1,993
Ending balance	8,196	6,220
Loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	2,051,191		2,124,820
Loans acquired with credit deterioration	2,549		2,586
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	2,053,740		2,127,406
Allowance for loan losses:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	8,196		8,493
Loans acquired with credit deterioration	0		0
Total Allowance for loan losses	8,196	6,220
Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	1,047	2,385
Charge-offs	(769)	0
Recoveries	15	0
Provision for loan losses	559	(43)
Ending balance	852	2,342
Loans:
Individually evaluated for impairment	2,325		2,325
Collectively evaluated for impairment	62,343		56,510
Loans acquired with credit deterioration	1,737		4,539
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	66,405		63,374
Allowance for loan losses:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	468		424
Loans acquired with credit deterioration	384		623
Total Allowance for loan losses	852	2,342
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	2,698	2,490
Charge-offs	0	(288)
Recoveries	0	224
Provision for loan losses	297	(119)
Ending balance	2,995	2,307
Loans:
Individually evaluated for impairment	1,800		1,820
Collectively evaluated for impairment	277,660		285,608
Loans acquired with credit deterioration	9,866		9,967
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	289,326		297,395
Allowance for loan losses:
Individually evaluated for impairment	185		188
Collectively evaluated for impairment	1,648		1,436
Loans acquired with credit deterioration	1,162		1,074
Total Allowance for loan losses	2,995	2,307
Manufactured housing
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	262	614
Charge-offs	0	0
Recoveries	0	0
Provision for loan losses	84	(21)
Ending balance	346	593
Loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	117,747		122,715
Loans acquired with credit deterioration	3,875		4,016
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	121,622		126,731
Allowance for loan losses:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	90		92
Loans acquired with credit deterioration	256		170
Total Allowance for loan losses	346	593
Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance	114	130
Charge-offs	(36)	0
Recoveries	83	2
Provision for loan losses	(52)	(5)
Ending balance	109	127
Loans:
Individually evaluated for impairment	73		135
Collectively evaluated for impairment	3,794		4,050
Loans acquired with credit deterioration	234		248
Loans And Leases Receivable Gross Carrying Amount Covered And Not Covered	4,101		4,433
Allowance for loan losses:
Individually evaluated for impairment	25		32
Collectively evaluated for impairment	30		28
Loans acquired with credit deterioration	54		54
Total Allowance for loan losses	$ 109	$ 127