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	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
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	4,473	$ 7,916
90 Days Or More Past Due	4,546	4,388
Total Past Due	9,019	12,304
Non-Accrual	7,736	7,487
Current	4,238,899	4,204,373
Purchased Credit-Impaired Loans	44,084	45,316
Total Loans	4,299,738	4,269,480
Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	481	665
90 Days Or More Past Due	0	0
Total Past Due	481	665
Non-Accrual	4,059	4,246
Current	24,735	25,969
Purchased Credit-Impaired Loans	8,090	11,301
Total Loans	37,365	42,181
Commercial real estate | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	288	0
90 Days Or More Past Due	0	0
Total Past Due	288	0
Non-Accrual	3,436	3,450
Current	1,147,262	1,101,119
Purchased Credit-Impaired Loans	26,739	27,503
Total Loans	1,177,725	1,132,072
Commercial real estate | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	25	0
90 Days Or More Past Due	0	0
Total Past Due	25	0
Non-Accrual	497	615
Current	10,765	11,884
Purchased Credit-Impaired Loans	5,060	5,086
Total Loans	16,347	17,585
Multi-family | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	0	0
Current	2,050,830	2,124,448
Purchased Credit-Impaired Loans	2,549	2,586
Total Loans	2,053,379	2,127,034
Multi-family | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	0	0
Current	361	372
Purchased Credit-Impaired Loans	0	0
Total Loans	361	372
Commercial and industrial | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	366
90 Days Or More Past Due	0	0
Total Past Due	0	366
Non-Accrual	2,307	2,257
Current	602,407	536,326
Purchased Credit-Impaired Loans	1,377	1,481
Total Loans	606,091	540,430
Commercial and industrial | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	26	518
90 Days Or More Past Due	0	0
Total Past Due	26	518
Non-Accrual	158	165
Current	825	361
Purchased Credit-Impaired Loans	737	1,191
Total Loans	1,746	2,235
Construction | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	0	0
Current	62,343	56,510
Purchased Credit-Impaired Loans	87	159
Total Loans	62,430	56,669
Construction | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	2,325	2,325
Current	0	0
Purchased Credit-Impaired Loans	1,650	4,380
Total Loans	3,975	6,705
Residential real estate | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	289	1,226
90 Days Or More Past Due	0	0
Total Past Due	289	1,226
Non-Accrual	946	849
Current	266,670	273,565
Purchased Credit-Impaired Loans	9,262	9,363
Total Loans	277,167	285,003
Residential real estate | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	294	0
90 Days Or More Past Due	0	0
Total Past Due	294	0
Non-Accrual	1,006	1,006
Current	10,255	10,782
Purchased Credit-Impaired Loans	604	604
Total Loans	12,159	12,392
Other | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	0	0
Current	1,129	1,333
Purchased Credit-Impaired Loans	195	208
Total Loans	1,324	1,541
Other | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	136	147
90 Days Or More Past Due	0	0
Total Past Due	136	147
Non-Accrual	73	135
Current	2,529	2,570
Purchased Credit-Impaired Loans	39	40
Total Loans	2,777	2,892
Manufactured housing | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	3,896	6,324
90 Days Or More Past Due	4,546	4,388
Total Past Due	8,442	10,712
Non-Accrual	1,047	931
Current	108,258	111,072
Purchased Credit-Impaired Loans	3,875	4,016
Total Loans	121,622	$ 126,731