Loans Receivable and Allowance for Loan Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	$ 5,907,315	$ 5,453,479
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	$ 6,807	9,149
90 Days or More Past Due	2,292	2,805
Total Past Due	9,099	11,954
Non-Accrual	16,114	10,771
Current	5,840,236	5,387,940
Purchased Credit-Impaired Loans	41,675	42,480
Total Loans	5,907,124	5,453,145
Non-covered Loans | Multi-family
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	3,206,569	2,905,789
Purchased Credit-Impaired Loans	3,608	3,650
Total Loans	3,210,177	2,909,439
Non-covered Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	4	39
90 Days or More Past Due	0	0
Total Past Due	4	39
Non-Accrual	6,035	1,973
Current	841,166	799,595
Purchased Credit-Impaired Loans	1,470	1,552
Total Loans	848,675	803,159
Non-covered Loans | Commercial real estate - owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	268
90 Days or More Past Due	0	0
Total Past Due	0	268
Non-Accrual	2,689	2,700
Current	296,285	292,312
Purchased Credit-Impaired Loans	12,740	12,961
Total Loans	311,714	308,241
Non-covered Loans | Commercial real estate - non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	1,997
90 Days or More Past Due	0	0
Total Past Due	0	1,997
Non-Accrual	2,610	1,307
Current	1,037,684	940,895
Purchased Credit-Impaired Loans	11,868	12,056
Total Loans	1,052,162	956,255
Non-covered Loans | Construction
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	102,827	87,006
Purchased Credit-Impaired Loans	234	234
Total Loans	103,061	87,240
Non-covered Loans | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	3,487	2,986
90 Days or More Past Due	0	0
Total Past Due	3,487	2,986
Non-Accrual	2,325	2,202
Current	253,006	257,984
Purchased Credit-Impaired Loans	8,213	8,441
Total Loans	267,031	271,613
Non-covered Loans | Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	3,296	3,752
90 Days or More Past Due	2,292	2,805
Total Past Due	5,588	6,557
Non-Accrual	2,356	2,449
Current	99,572	101,132
Purchased Credit-Impaired Loans	3,314	3,352
Total Loans	110,830	113,490
Non-covered Loans | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	20	107
90 Days or More Past Due	0	0
Total Past Due	20	107
Non-Accrual	99	140
Current	3,127	3,227
Purchased Credit-Impaired Loans	228	234
Total Loans	$ 3,474	$ 3,708