Loans Receivable and Allowance for Loan Losses - Summary of Aging Loans Receivable by Portfolio Segment and Class (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	$ 40,194	$ 25,690
90 days or more past due and accruing	0	0
Total  Past Due	52,769	51,273
Current	7,284,795	7,202,629
Total gross loans	7,337,564	7,253,902
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	9,564	5,851
Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	3,011	19,732
Mortgage Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	13,813	9,033
90 days or more past due and accruing	0	0
Total  Past Due	22,297	18,778
Current	5,289,148	5,108,675
Total gross loans	5,311,445	5,127,453
Mortgage Portfolio Segment | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	8,543	5,853
90 days or more past due and accruing	0	0
Total  Past Due	17,027	15,598
Current	1,060,662	1,083,866
Total gross loans	1,077,689	1,099,464
Mortgage Portfolio Segment | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	5,270	3,180
90 days or more past due and accruing	0	0
Total  Past Due	5,270	3,180
Current	2,573,123	2,296,133
Total gross loans	2,578,393	2,299,313
Mortgage Portfolio Segment | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	0	0
90 days or more past due and accruing	0	0
Total  Past Due	0	0
Current	1,225,551	1,339,677
Total gross loans	1,225,551	1,339,677
Mortgage Portfolio Segment | Construction Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	0	0
90 days or more past due and accruing	0	0
Total  Past Due	0	0
Current	429,812	388,999
Total gross loans	429,812	388,999
Mortgage Portfolio Segment | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	5,905	4,188
Mortgage Portfolio Segment | Financing Receivables, 30 to 59 Days Past Due | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	5,905	4,188
Mortgage Portfolio Segment | Financing Receivables, 30 to 59 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	0	0
Mortgage Portfolio Segment | Financing Receivables, 30 to 59 Days Past Due | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	0	0
Mortgage Portfolio Segment | Financing Receivables, 30 to 59 Days Past Due | Construction Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	0	0
Mortgage Portfolio Segment | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	2,579	5,557
Mortgage Portfolio Segment | Financing Receivables, 60 to 89 Days Past Due | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	2,579	5,557
Mortgage Portfolio Segment | Financing Receivables, 60 to 89 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	0	0
Mortgage Portfolio Segment | Financing Receivables, 60 to 89 Days Past Due | Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	0	0
Mortgage Portfolio Segment | Financing Receivables, 60 to 89 Days Past Due | Construction Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	0	0
Commercial Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	25,160	15,391
90 days or more past due and accruing	0	0
Total  Past Due	27,638	29,381
Current	1,607,121	1,665,640
Total gross loans	1,634,759	1,695,021
Commercial Portfolio Segment | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	2,383	425
Commercial Portfolio Segment | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	95	13,565
Consumer Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,221	1,266
90 days or more past due and accruing	0	0
Total  Past Due	2,834	3,114
Current	388,526	428,314
Total gross loans	391,360	431,428
Consumer Portfolio Segment | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	1,276	1,238
Consumer Portfolio Segment | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable past due	$ 337	$ 610