Loans Receivable and Allowance for Credit Losses (Summary of Aging Loans Receivable by Portfolio Segment and Class) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	$ 9,568,028	$ 9,839,858
Non-accrual	66,201	87,090
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	78,963	125,100
Non-accrual loans with no related allowance	49,924	49,013
Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,230,018	1,294,702
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	3,704,684	3,458,666
Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,379,773	1,484,515
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	685,792	541,939
30 to 59 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	9,557	22,762
60 to 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	3,205	15,248
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	9,489,065	9,714,758
Mortgage Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	7,000,267	6,779,822
Non-accrual	43,288	42,689
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	51,225	68,995
Non-accrual loans with no related allowance	33,286	31,189
Mortgage Portfolio Segment | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,230,018	1,294,702
Non-accrual	7,263	9,315
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	14,107	33,956
Non-accrual loans with no related allowance	7,263	9,315
Mortgage Portfolio Segment | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	3,704,684	3,458,666
Non-accrual	32,619	31,982
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	33,462	32,856
Non-accrual loans with no related allowance	22,617	20,482
Mortgage Portfolio Segment | Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,379,773	1,484,515
Non-accrual	439	0
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	689	791
Non-accrual loans with no related allowance	439	0
Mortgage Portfolio Segment | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	685,792	541,939
Non-accrual	2,967	1,392
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	2,967	1,392
Non-accrual loans with no related allowance	2,967	1,392
Mortgage Portfolio Segment | 30 to 59 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	5,760	16,756
Mortgage Portfolio Segment | 30 to 59 Days | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	4,667	15,789
Mortgage Portfolio Segment | 30 to 59 Days | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	843	761
Mortgage Portfolio Segment | 30 to 59 Days | Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	250	206
Mortgage Portfolio Segment | 30 to 59 Days | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	0	0
Mortgage Portfolio Segment | 60 to 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	2,177	9,550
Mortgage Portfolio Segment | 60 to 89 Days | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	2,177	8,852
Mortgage Portfolio Segment | 60 to 89 Days | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	0	113
Mortgage Portfolio Segment | 60 to 89 Days | Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	0	585
Mortgage Portfolio Segment | 60 to 89 Days | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	0	0
Mortgage Portfolio Segment | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	6,949,042	6,710,827
Mortgage Portfolio Segment | Current | Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,215,911	1,260,746
Mortgage Portfolio Segment | Current | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	3,671,222	3,425,810
Mortgage Portfolio Segment | Current | Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,379,084	1,483,724
Mortgage Portfolio Segment | Current | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	682,825	540,547
Commercial Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	2,234,020	2,567,470
Non-accrual	21,434	42,118
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	24,130	44,955
Non-accrual loans with no related allowance	15,159	15,541
Commercial Loans | 30 to 59 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,668	1,658
Commercial Loans | 60 to 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	1,028	1,179
Commercial Loans | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	2,209,890	2,522,515
Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	333,741	492,566
Non-accrual	1,479	2,283
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	3,608	11,150
Non-accrual loans with no related allowance	1,479	2,283
Consumer Loans | 30 to 59 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	2,129	4,348
Consumer Loans | 60 to 89 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	0	4,519
Consumer Loans | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total gross loans	$ 330,133	$ 481,416