Loans Receivable and Allowance for Loan Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 6,699	$ 11,954
Non-Accrual	13,396	10,771
Current	5,961,730	5,387,940
Loans receivable	6,016,995	5,453,479
Loans receivable, gross	$ 6,016,899	5,453,145
Due days for loan payments	30 days
Delinquent period	90 days
Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 35,074	42,480
30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,156	9,149
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,543	2,805
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Non-Accrual	0	0
Current	3,147,521	2,905,789
Loans receivable, gross	3,150,298	2,909,439
Multi-family | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	2,777	3,650
Multi-family | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Multi-family | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	39
Non-Accrual	4,900	1,973
Current	899,200	799,595
Loans receivable, gross	905,250	803,159
Commercial and industrial | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	1,150	1,552
Commercial and industrial | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	39
Commercial and industrial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial real estate - owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	268
Non-Accrual	2,071	2,700
Current	376,482	292,312
Loans receivable, gross	391,471	308,241
Commercial real estate - owner occupied | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	12,918	12,961
Commercial real estate - owner occupied | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	268
Commercial real estate - owner occupied | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial real estate - non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,997
Non-Accrual	2,152	1,307
Current	1,142,024	940,895
Loans receivable, gross	1,151,099	956,255
Commercial real estate - non-owner occupied | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	6,923	12,056
Commercial real estate - non-owner occupied | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,997
Commercial real estate - non-owner occupied | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Non-Accrual	0	0
Current	83,835	87,006
Loans receivable, gross	83,835	87,240
Construction | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	0	234
Construction | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,182	2,986
Non-Accrual	2,238	2,202
Current	215,766	257,984
Loans receivable, gross	227,122	271,613
Residential real estate | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	7,936	8,441
Residential real estate | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,182	2,986
Residential real estate | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,501	6,557
Non-Accrual	1,992	2,449
Current	93,784	101,132
Loans receivable, gross	104,404	113,490
Manufactured housing | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	3,127	3,352
Manufactured housing | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,958	3,752
Manufactured housing | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,543	2,805
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16	107
Non-Accrual	43	140
Current	3,118	3,227
Loans receivable, gross	3,420	3,708
Other | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	243	234
Other | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16	107
Other | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0