Loans Receivable and Allowance for Loan Losses - Credit Quality Tables for Covered and Non-Covered Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	$ 4,269,480	$ 2,399,265
Total loan receivable covered under FDIC loss sharing agreements	42,181	66,725
Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	4,269,480	2,399,265
Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	42,181	66,725
Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	4,101,356	2,215,827
Pass/Satisfactory | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	22,668	34,122
Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	29,483	24,044
Special Mention | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	5,076	3,668
Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	10,369	17,779
Substandard | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	11,545	25,642
Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	116,629	129,474
Performing | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	2,610	3,226
Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	11,643	12,141
Nonperforming | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	282	67
Commercial and industrial | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	540,430	292,937
Commercial and industrial | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	2,235	3,658
Commercial and industrial | Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	524,848	277,491
Commercial and industrial | Pass/Satisfactory | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	1,104	1,582
Commercial and industrial | Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	13,238	10,175
Commercial and industrial | Special Mention | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	106
Commercial and industrial | Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	2,344	5,271
Commercial and industrial | Substandard | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	1,131	1,970
Commercial and industrial | Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Commercial and industrial | Performing | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Commercial and industrial | Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Commercial and industrial | Nonperforming | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Commercial real estate | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	1,132,072	724,752
Commercial real estate | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	17,585	28,839
Commercial real estate | Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	1,109,565	703,636
Commercial real estate | Pass/Satisfactory | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	10,207	17,803
Commercial real estate | Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	16,002	11,995
Commercial real estate | Special Mention | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	5,076	3,107
Commercial real estate | Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	6,505	9,121
Commercial real estate | Substandard | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	2,302	7,929
Commercial real estate | Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Commercial real estate | Performing | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Commercial real estate | Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Commercial real estate | Nonperforming | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Multi-family | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	2,127,034	1,063,459
Multi-family | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	372	600
Multi-family | Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	2,127,034	1,062,411
Multi-family | Pass/Satisfactory | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	372	600
Multi-family | Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	905
Multi-family | Special Mention | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Multi-family | Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	143
Multi-family | Substandard | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Multi-family | Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Multi-family | Performing | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Multi-family | Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Multi-family | Nonperforming | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Construction | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	56,669	31,314
Construction | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	6,705	11,603
Construction | Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	56,669	29,701
Construction | Pass/Satisfactory | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Construction | Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	29
Construction | Special Mention | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Construction | Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	1,584
Construction | Substandard | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	6,705	11,603
Construction | Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Construction | Performing | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Construction | Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Construction | Nonperforming | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Residential Real Estate | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	285,003	145,188
Residential Real Estate | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	12,392	18,732
Residential Real Estate | Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	283,240	142,588
Residential Real Estate | Pass/Satisfactory | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	10,985	14,137
Residential Real Estate | Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	243	940
Residential Real Estate | Special Mention | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	455
Residential Real Estate | Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	1,520	1,660
Residential Real Estate | Substandard | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	1,407	4,140
Residential Real Estate | Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Residential Real Estate | Performing | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Residential Real Estate | Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Residential Real Estate | Nonperforming | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Home equity / other | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	1,541	2,144
Home equity / other | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	2,892	3,293
Home equity / other | Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Home equity / other | Pass/Satisfactory | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Home equity / other | Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Home equity / other | Special Mention | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Home equity / other | Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Home equity / other | Substandard | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	0	0
Home equity / other | Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	1,541	2,144
Home equity / other | Performing | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	2,610	3,226
Home equity / other | Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Home equity / other | Nonperforming | Covered Loan
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable covered under FDIC loss sharing agreements	282	67
Manufactured Housing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	126,731	139,471
Manufactured Housing | Pass/Satisfactory | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Manufactured Housing | Special Mention | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Manufactured Housing | Substandard | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	0	0
Manufactured Housing | Performing | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	115,088	127,330
Manufactured Housing | Nonperforming | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total loan receivable not covered under FDIC loss sharing agreements	$ 11,643	$ 12,141