Loans Receivable and Allowance for Loan Losses (Summary of Aging Loans Receivable by Portfolio Segment and Class) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	$ 24,797	$ 25,690
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	57,993	51,273
Current	7,168,987	7,202,629
Total gross loans	7,226,980	7,253,902
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	29,233	5,851
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	3,963	19,732
Mortgage Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	8,325	9,033
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	19,616	18,778
Current	5,087,848	5,108,675
Total gross loans	5,107,464	5,127,453
Mortgage Portfolio Segment [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	6,809	5,853
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	16,482	15,598
Current	1,070,702	1,083,866
Total gross loans	1,087,184	1,099,464
Mortgage Portfolio Segment [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,516	3,180
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	3,134	3,180
Current	2,285,208	2,296,133
Total gross loans	2,288,342	2,299,313
Mortgage Portfolio Segment [Member] | Multi-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	0	0
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	0	0
Current	1,357,038	1,339,677
Total gross loans	1,357,038	1,339,677
Mortgage Portfolio Segment [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	0	0
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	0	0
Current	374,900	388,999
Total gross loans	374,900	388,999
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	7,425	4,188
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	6,132	4,188
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	1,293	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Multi-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	3,866	5,557
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	3,541	5,557
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	325	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Multi-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	14,785	15,391
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	35,144	29,381
Current	1,663,002	1,665,640
Total gross loans	1,698,146	1,695,021
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	20,350	425
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	9	13,565
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,687	1,266
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	3,233	3,114
Current	418,137	428,314
Total gross loans	421,370	431,428
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	1,458	1,238
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	$ 88	$ 610