Loans Receivable and Allowance for Loan Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	$ 6,016,899	$ 5,453,145
Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	5,846,309	5,294,352
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	41,102	24,506
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	21,664	17,089
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	100,272	107,945
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,552	9,253
Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,150,298	2,909,439
Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,145,089	2,907,362
Multi-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	379	661
Multi-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	4,830	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	905,250	803,159
Commercial and industrial | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	874,940	784,892
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	23,147	14,052
Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,163	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	391,471	308,241
Commercial real estate - owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	377,917	295,762
Commercial real estate - owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	9,032	7,840
Commercial real estate - owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	4,522	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	1,151,099	956,255
Commercial real estate - non-owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	1,140,415	950,886
Commercial real estate - non-owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	8,544	1,671
Commercial real estate - non-owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	2,140	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	83,835	87,240
Construction | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	83,835	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	227,122	271,613
Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	224,113	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	3,009	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	104,404	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	96,911	104,484
Manufactured housing | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,493	9,006
Other
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,420	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	3,361	3,461
Other | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	$ 59	$ 247