Loans Receivable and Allowance for Loan Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	$ 4,299,738	$ 4,269,480
Loans receivable, covered	37,365	42,181
Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	37,365	42,181
Covered Loans | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	22,291	22,668
Covered Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	4,046	5,076
Covered Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	8,251	11,545
Covered Loans | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	2,568	2,610
Covered Loans | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	209	282
Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	1,746	2,235
Covered Loans | Commercial and industrial | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	1,061	1,104
Covered Loans | Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	685	1,131
Covered Loans | Commercial and industrial | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial and industrial | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	16,347	17,585
Covered Loans | Commercial real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	10,117	10,207
Covered Loans | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	4,046	5,076
Covered Loans | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	2,184	2,302
Covered Loans | Commercial real estate | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Commercial real estate | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	0	0
Covered Loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	361	372
Covered Loans | Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	361	372
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	0
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 | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	3,975	6,705
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	3,975	6,705
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	12,159	12,392
Covered Loans | Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	10,752	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	1,407	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	2,777	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	2,568	2,610
Covered Loans | Other | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, covered	209	282
Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,299,738	4,269,480
Non-covered Loans | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	4,143,890	4,101,356
Non-covered Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	22,092	29,483
Non-covered Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	10,810	10,369
Non-covered Loans | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	113,457	116,629
Non-covered Loans | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	9,489	11,643
Non-covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	606,091	540,430
Non-covered Loans | Commercial and industrial | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	592,072	524,848
Non-covered Loans | Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	11,484	13,238
Non-covered Loans | Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	2,535	2,344
Non-covered Loans | Commercial and industrial | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial and industrial | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,177,725	1,132,072
Non-covered Loans | Commercial real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,160,583	1,109,565
Non-covered Loans | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	10,608	16,002
Non-covered Loans | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	6,534	6,505
Non-covered Loans | Commercial real estate | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Commercial real estate | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	0	0
Non-covered Loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	2,053,379	2,127,034
Non-covered Loans | Multi-family | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	2,053,379	2,127,034
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 | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	62,430	56,669
Non-covered Loans | Construction | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	62,430	56,669
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	277,167	285,003
Non-covered Loans | Residential real estate | Pass/Satisfactory
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	275,426	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	1,741	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 | Other
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	1,324	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	1,324	1,541
Non-covered Loans | Other | 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	121,622	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	112,133	115,088
Non-covered Loans | Manufactured housing | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans receivable, non-covered	$ 9,489	$ 11,643