Loans Receivable and Allowance for Loan Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
PCI Loans	$ 40,325	$ 39,280
Due days for loan payments	30 days
Delinquent period	90 days
Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	7,916	8,486
90 Or More Days Past Due	4,388	3,772
Total Past Due Still Accruing	12,304	12,258
Non-Accrual	7,487	13,513
Current	4,204,373	2,317,687
PCI Loans	45,316	55,807
Total Loans	4,269,480	2,399,265
Covered Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	665	686
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	665	686
Non-Accrual	4,246	5,650
Current	25,969	35,914
PCI Loans	11,301	24,475
Total Loans	42,181	66,725
Commercial real estate | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	0
Non-Accrual	3,450	5,948
Current	1,101,119	685,999
PCI Loans	27,503	32,805
Total Loans	1,132,072	724,752
Commercial real estate | Covered Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	362
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	362
Non-Accrual	615	2,599
Current	11,884	17,059
PCI Loans	5,086	8,819
Total Loans	17,585	28,839
Multi-family | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	0
Non-Accrual	0	0
Current	2,124,448	1,060,137
PCI Loans	2,586	3,322
Total Loans	2,127,034	1,063,459
Multi-family | Covered Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	0
Non-Accrual	0	0
Current	372	600
PCI Loans	0	0
Total Loans	372	600
Commercial and industrial | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	366	10
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	366	10
Non-Accrual	2,257	4,564
Current	536,326	284,767
PCI Loans	1,481	3,596
Total Loans	540,430	292,937
Commercial and industrial | Covered Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	518	178
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	518	178
Non-Accrual	165	151
Current	361	1,067
PCI Loans	1,191	2,262
Total Loans	2,235	3,658
Construction | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	0
Non-Accrual	0	1,584
Current	56,510	29,482
PCI Loans	159	248
Total Loans	56,669	31,314
Construction | Covered Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	0
Non-Accrual	2,325	2,325
Current	0	0
PCI Loans	4,380	9,278
Total Loans	6,705	11,603
Residential Real Estate | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	1,226	555
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	1,226	555
Non-Accrual	849	969
Current	273,565	133,158
PCI Loans	9,363	10,506
Total Loans	285,003	145,188
Residential Real Estate | Covered Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	90
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	90
Non-Accrual	1,006	564
Current	10,782	14,107
PCI Loans	604	3,971
Total Loans	12,392	18,732
Home equity / other | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	0	0
Non-Accrual	0	0
Current	1,333	1,728
PCI Loans	208	416
Total Loans	1,541	2,144
Home equity / other | Covered Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	147	56
90 Or More Days Past Due	0	0
Total Past Due Still Accruing	147	56
Non-Accrual	135	11
Current	2,570	3,081
PCI Loans	40	145
Total Loans	2,892	3,293
Manufactured Housing | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	6,324	7,921
90 Or More Days Past Due	4,388	3,772
Total Past Due Still Accruing	10,712	11,693
Non-Accrual	931	448
Current	111,072	122,416
PCI Loans	4,016	4,914
Total Loans	$ 126,731	$ 139,471