Loans Receivable and Allowance for Loan Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	$ 4,492,206	$ 4,269,480
Loans receivable, covered	31,689	42,181
Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,492,206	4,269,480
Non-covered Loans | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,338,701	4,101,358
Non-covered Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	23,275	29,482
Non-covered Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	9,203	10,368
Non-covered Loans | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	112,645	116,629
Non-covered Loans | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	8,382	11,643
Non-covered Loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	2,236,757	2,206,403
Non-covered Loans | Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	2,236,757	2,206,403
Non-covered Loans | Multi-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Multi-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	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	652,214	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	638,293	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	11,841	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	2,080	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	261,684	229,828
Non-covered Loans | Commercial real estate owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	250,887	212,326
Non-covered Loans | Commercial real estate owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	6,387	12,352
Non-covered Loans | Commercial real estate owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,410	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	886,982	827,940
Non-covered Loans | Commercial real estate non-owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	881,058	824,279
Non-covered Loans | Commercial real estate non-owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	5,047	2,322
Non-covered Loans | Commercial real estate non-owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	877	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	68,073	44,642
Non-covered Loans | Construction | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	68,073	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	265,469	285,003
Non-covered Loans | Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	263,633	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	1,836	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	119,786	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	111,405	115,088
Non-covered Loans | Manufactured housing | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	8,381	11,643
Non-covered Loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,241	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	1,240	1,541
Non-covered Loans | Other | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1	0
Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	31,689	42,181
Covered Loans | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	20,179	22,669
Covered Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	3,978	5,076
Covered Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	4,811	11,544
Covered Loans | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	2,514	2,610
Covered Loans | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	207	282
Covered Loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	1,730	2,002
Covered Loans | Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	355	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	1,375	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	1,203	2,543
Covered Loans | Commercial and industrial (including owner occupied commercial real estate) | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	1,057	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	146	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	5,382	5,906
Covered Loans | Commercial real estate owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	4,636	5,030
Covered Loans | Commercial real estate owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	691	704
Covered Loans | Commercial real estate owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	55	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	8,798	11,370
Covered Loans | Commercial real estate non-owner occupied | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	4,643	4,959
Covered Loans | Commercial real estate non-owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	3,287	4,372
Covered Loans | Commercial real estate non-owner occupied | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	868	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	669	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	669	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	11,186	12,392
Covered Loans | Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	9,488	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	1,698	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	2,721	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	2,514	2,610
Covered Loans | Other | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	$ 207	$ 282