Loans Receivable and Allowance for Loan Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	$ 5,907,124	$ 5,453,145
Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	5,907,124	5,453,145
Non-covered Loans | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	5,742,155	5,294,352
Non-covered Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	30,696	24,506
Non-covered Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	19,969	17,089
Non-covered Loans | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	106,241	107,945
Non-covered Loans | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	8,063	9,253
Non-covered Loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,210,177	2,909,439
Non-covered Loans | Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,208,368	2,907,362
Non-covered Loans | Multi-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	393	661
Non-covered Loans | Multi-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	1,416	1,416
Non-covered Loans | Multi-family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Multi-family | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	848,675	803,159
Non-covered Loans | Commercial and industrial | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	820,836	784,892
Non-covered Loans | Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	19,911	14,052
Non-covered Loans | Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,928	4,215
Non-covered Loans | Commercial and industrial | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Commercial and industrial | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Commercial real estate - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	311,714	308,241
Non-covered Loans | Commercial real estate - owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	299,042	295,762
Non-covered Loans | Commercial real estate - owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	8,059	7,840
Non-covered Loans | Commercial real estate - owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	4,613	4,639
Non-covered Loans | Commercial real estate - owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Commercial real estate - owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Commercial real estate - non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	1,052,162	956,255
Non-covered Loans | Commercial real estate - non-owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	1,047,331	950,886
Non-covered Loans | Commercial real estate - non-owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	2,053	1,671
Non-covered Loans | Commercial real estate - non-owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	2,778	3,698
Non-covered Loans | Commercial real estate - non-owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Commercial real estate - non-owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	103,061	87,240
Non-covered Loans | Construction | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	103,061	87,240
Non-covered Loans | Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Construction | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Construction | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	267,031	271,613
Non-covered Loans | Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	263,517	268,210
Non-covered Loans | Residential real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	280	282
Non-covered Loans | Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,234	3,121
Non-covered Loans | Residential real estate | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Residential real estate | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Manufactured housing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	110,830	113,490
Non-covered Loans | Manufactured housing | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Manufactured housing | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Manufactured housing | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Manufactured housing | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	102,886	104,484
Non-covered Loans | Manufactured housing | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	7,944	9,006
Non-covered Loans | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,474	3,708
Non-covered Loans | Other consumer | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Other consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	0	0
Non-covered Loans | Other consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	3,355	3,461
Non-covered Loans | Other consumer | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, gross	$ 119	$ 247