Loans Receivable and Allowance for Loan Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 8,955	$ 19,813
Non-Accrual	25,995	26,415
Current	7,121,560	6,695,032
Loans receivable, gross	$ 7,181,084	6,768,175
Delinquent period	30 days
Due days for loan payments	90 days
Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	$ 24,574	26,915
30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,294	17,070
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,661	2,743
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	4,900
Non-Accrual	1,343	0
Current	3,539,640	3,495,600
Loans receivable, gross	3,542,770	3,502,381
Multi-family | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	1,787	1,881
Multi-family | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	4,900
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	1,087	103
Non-Accrual	13,683	17,392
Current	1,251,148	1,130,831
Loans receivable, gross	1,266,520	1,149,090
Commercial and industrial | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	602	764
Commercial and industrial | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,087	103
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	202
Non-Accrual	718	1,453
Current	534,923	472,501
Loans receivable, gross	545,231	484,728
Commercial real estate - owner occupied | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	9,590	10,572
Commercial real estate - owner occupied | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	202
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	93
Non-Accrual	2,536	160
Current	1,148,581	1,213,216
Loans receivable, gross	1,155,998	1,218,719
Commercial real estate - non-owner occupied | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	4,881	5,250
Commercial real estate - non-owner occupied | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	93
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	88,141	85,393
Loans receivable, gross	88,141	85,393
Construction | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	0	0
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	2,174	7,628
Non-Accrual	5,606	5,420
Current	480,381	215,361
Loans receivable, gross	493,222	234,090
Residential real estate | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	5,061	5,681
Residential real estate | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,174	7,628
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	5,638	6,771
Non-Accrual	2,015	1,959
Current	75,250	78,946
Loans receivable, gross	85,328	90,227
Manufactured housing | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	2,425	2,551
Manufactured housing | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,977	4,028
Manufactured housing | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,661	2,743
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	56	116
Non-Accrual	94	31
Current	3,496	3,184
Loans receivable, gross	3,874	3,547
Other | Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	228	216
Other | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	56	116
Other | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0