Loans Receivable and Allowance for Loan Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	$ 4,754,730	$ 4,269,480
Loans receivable, covered	13,849	42,181
Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,754,730	4,269,480
Non-covered Loans | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,592,212	4,101,358
Non-covered Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	25,860	29,482
Non-covered Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	18,840	10,368
Non-covered Loans | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	108,933	116,629
Non-covered Loans | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	8,885	11,643
Non-covered Loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	2,405,400	2,206,403
Non-covered Loans | Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	2,403,599	2,206,403
Non-covered Loans | Multi-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	405	0
Non-covered Loans | Multi-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,396	0
Non-covered Loans | Multi-family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Multi-family | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial and industrial (including owner occupied commercial real estate)
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	683,940	547,392
Non-covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	665,484	530,468
Non-covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	11,822	14,565
Non-covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	6,634	2,359
Non-covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial real estate owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	284,018	229,828
Non-covered Loans | Commercial real estate owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	270,857	212,326
Non-covered Loans | Commercial real estate owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	9,007	12,352
Non-covered Loans | Commercial real estate owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,154	5,150
Non-covered Loans | Commercial real estate owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial real estate owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial real estate non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	912,971	827,940
Non-covered Loans | Commercial real estate non-owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	903,357	824,279
Non-covered Loans | Commercial real estate non-owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,626	2,322
Non-covered Loans | Commercial real estate non-owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,988	1,339
Non-covered Loans | Commercial real estate non-owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial real estate non-owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	89,616	44,642
Non-covered Loans | Construction | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	89,616	44,642
Non-covered Loans | Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Construction | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Construction | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	260,967	285,003
Non-covered Loans | Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	259,299	283,240
Non-covered Loans | Residential real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	243
Non-covered Loans | Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,668	1,520
Non-covered Loans | Residential real estate | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Residential real estate | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Manufactured housing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	116,742	126,731
Non-covered Loans | Manufactured housing | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Manufactured housing | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Manufactured housing | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Manufactured housing | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	107,857	115,088
Non-covered Loans | Manufactured housing | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	8,885	11,643
Non-covered Loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,076	1,541
Non-covered Loans | Other | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Other | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Other | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Other | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,076	1,541
Non-covered Loans | Other | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	13,849	42,181
Covered Loans | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	9,733	22,669
Covered Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	5,076
Covered Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	1,448	11,544
Covered Loans | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	2,447	2,610
Covered Loans | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	221	282
Covered Loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	2,002
Covered Loans | Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	373
Covered Loans | Multi-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Multi-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	1,629
Covered Loans | Multi-family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Multi-family | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial and industrial (including owner occupied commercial real estate)
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	2,543
Covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	1,322
Covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	1,221
Covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial real estate owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	5,906
Covered Loans | Commercial real estate owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	5,030
Covered Loans | Commercial real estate owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	704
Covered Loans | Commercial real estate owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	172
Covered Loans | Commercial real estate owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial real estate owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial real estate non-owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	11,370
Covered Loans | Commercial real estate non-owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	4,959
Covered Loans | Commercial real estate non-owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	4,372
Covered Loans | Commercial real estate non-owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	2,039
Covered Loans | Commercial real estate non-owner occupied | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial real estate non-owner occupied | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	5,076
Covered Loans | Construction | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	5,076
Covered Loans | Construction | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Construction | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	11,181	12,392
Covered Loans | Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	9,733	10,985
Covered Loans | Residential real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	1,448	1,407
Covered Loans | Residential real estate | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Residential real estate | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	2,668	2,892
Covered Loans | Other | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Other | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Other | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Other | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	2,447	2,610
Covered Loans | Other | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	$ 221	$ 282