Loans Receivable and Allowance for Loan Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	$ 6,114,274	$ 5,453,145
Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	5,951,315	5,294,352
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	33,618	24,506
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	18,190	17,089
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	103,530	107,945
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,621	9,253
Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,308,556	2,909,439
Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,306,759	2,907,362
Multi-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	386	661
Multi-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	1,411	1,416
Multi-family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Multi-family | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	843,868	803,159
Commercial and industrial | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	815,210	784,892
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	21,588	14,052
Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,070	4,215
Commercial and industrial | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Commercial and industrial | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Commercial real estate - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	348,806	308,241
Commercial real estate - owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	336,283	295,762
Commercial real estate - owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,944	7,840
Commercial real estate - owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	4,579	4,639
Commercial real estate - owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Commercial real estate - owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Commercial real estate - non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	1,139,711	956,255
Commercial real estate - non-owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	1,133,554	950,886
Commercial real estate - non-owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,700	1,671
Commercial real estate - non-owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	2,457	3,698
Commercial real estate - non-owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Commercial real estate - non-owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Construction
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	99,615	87,240
Construction | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	99,615	87,240
Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Construction | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Construction | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	262,567	271,613
Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	259,894	268,210
Residential real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	282
Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	2,673	3,121
Residential real estate | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Residential real estate | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Manufactured housing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	107,874	113,490
Manufactured housing | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Manufactured housing | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Manufactured housing | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Manufactured housing | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	100,298	104,484
Manufactured housing | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,576	9,006
Other
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,277	3,708
Other | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Other | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Other | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Other | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,232	3,461
Other | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	$ 45	$ 247