Loans Receivable and Allowance for Credit Losses (Summary of Loans Receivable by Credit Quality Risk Rating Indicator) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 1,251,750	$ 1,959,045
2020	1,543,509	1,490,727
2019	1,417,019	1,155,196
2018	976,969	1,065,179
2017	888,363	796,248
Prior to 2017	2,804,798	2,625,267
Revolving Loans	586,832	647,390
Revolving loans to term loans	98,788	100,806
Total gross loans	9,568,028	9,839,858
Total classified and criticized
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,980	2,180
2020	7,118	63,409
2019	60,973	79,404
2018	68,917	93,346
2017	80,910	74,322
Prior to 2017	218,671	242,814
Revolving Loans	25,639	42,076
Revolving loans to term loans	6,062	8,410
Total gross loans	470,270	605,960
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,980	1,991
2020	6,590	50,756
2019	52,755	67,198
2018	32,088	53,276
2017	56,063	18,529
Prior to 2017	84,196	119,705
Revolving Loans	4,304	24,049
Revolving loans to term loans	3,465	5,113
Total gross loans	241,440	340,617
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	189
2020	528	12,653
2019	8,218	12,206
2018	36,829	40,070
2017	24,847	55,793
Prior to 2017	134,475	123,109
Revolving Loans	21,335	17,975
Revolving loans to term loans	2,597	3,296
Total gross loans	228,829	265,291
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	52
Revolving loans to term loans	0	0
Total gross loans	0	52
Loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020		0
2019		0
2018		0
2017		0
Prior to 2017		0
Revolving Loans		0
Revolving loans to term loans		0
Total gross loans		0
Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,249,770	1,956,865
2020	1,536,391	1,427,318
2019	1,356,046	1,075,792
2018	908,052	971,833
2017	807,453	721,926
Prior to 2017	2,586,127	2,382,453
Revolving Loans	561,193	605,314
Revolving loans to term loans	92,727	92,396
Total gross loans	9,097,759	9,233,898
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
2021	199,446	272,022
2020	246,325	155,492
2019	121,486	95,257
2018	71,177	104,164
2017	79,386	121,870
Prior to 2017	512,198	545,897
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	1,230,018	1,294,702
Residential \| Total classified and criticized
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	164
2020	0	3,375
2019	0	1,669
2018	280	2,221
2017	1,694	2,307
Prior to 2017	10,720	19,798
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	12,694	29,534
Residential \| Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	1,211	123
Prior to 2017	589	2,759
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	1,800	2,882
Residential \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	164
2020	0	3,375
2019	0	1,669
2018	280	2,221
2017	483	2,184
Prior to 2017	10,131	17,039
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	10,894	26,652
Residential \| Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Residential \| Loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Residential \| Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
2021	199,446	271,858
2020	246,325	152,117
2019	121,486	93,588
2018	70,897	101,943
2017	77,692	119,563
Prior to 2017	501,478	526,099
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	1,217,324	1,265,168
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	444,371	596,364
2020	598,059	632,077
2019	628,599	432,413
2018	383,948	476,523
2017	455,928	315,260
Prior to 2017	1,075,194	906,212
Revolving Loans	92,530	68,650
Revolving loans to term loans	26,055	31,167
Total gross loans	3,704,684	3,458,666
Commercial \| Total classified and criticized
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	1,797	31,173
2019	30,642	37,133
2018	56,264	43,933
2017	31,323	13,226
Prior to 2017	96,100	96,433
Revolving Loans	2,019	0
Revolving loans to term loans	0	1,045
Total gross loans	218,145	222,943
Commercial \| Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	1,797	29,268
2019	30,621	33,446
2018	28,757	22,838
2017	23,089	3,041
Prior to 2017	42,003	34,992
Revolving Loans	1,094	0
Revolving loans to term loans	0	1,045
Total gross loans	127,361	124,630
Commercial \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	1,905
2019	21	3,687
2018	27,507	21,095
2017	8,234	10,185
Prior to 2017	54,097	61,441
Revolving Loans	926	0
Revolving loans to term loans	0	0
Total gross loans	90,785	98,313
Commercial \| Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Commercial \| Loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Commercial \| Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
2021	444,371	596,364
2020	596,262	600,904
2019	597,957	395,280
2018	327,684	432,590
2017	424,605	302,034
Prior to 2017	979,094	809,779
Revolving Loans	90,511	68,650
Revolving loans to term loans	26,055	30,122
Total gross loans	3,486,539	3,235,723
Multi-Family
Financing Receivable, Credit Quality Indicator [Line Items]
2021	74,438	291,995
2020	303,779	180,953
2019	176,961	207,717
2018	192,255	172,427
2017	141,834	136,855
Prior to 2017	485,990	488,517
Revolving Loans	2,894	3,418
Revolving loans to term loans	1,622	2,633
Total gross loans	1,379,773	1,484,515
Multi-Family \| Total classified and criticized
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	439	682
2019	1,829	19,837
2018	0	3,117
2017	3,072	5,558
Prior to 2017	1,701	1,868
Revolving Loans	0	0
Revolving loans to term loans	0	288
Total gross loans	7,041	31,350
Multi-Family \| Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	682
2019	673	19,837
2018	0	3,117
2017	3,072	5,558
Prior to 2017	279	300
Revolving Loans	0	0
Revolving loans to term loans	0	288
Total gross loans	4,024	29,782
Multi-Family \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	439	0
2019	1,156	0
2018	0	0
2017	0	0
Prior to 2017	1,422	1,568
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	3,017	1,568
Multi-Family \| Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Multi-Family \| Loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Multi-Family \| Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
2021	74,438	291,995
2020	303,340	180,271
2019	175,132	187,880
2018	192,255	169,310
2017	138,762	131,297
Prior to 2017	484,289	486,649
Revolving Loans	2,894	3,418
Revolving loans to term loans	1,622	2,346
Total gross loans	1,372,732	1,453,165
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
2021	114,736	90,768
2020	158,026	250,529
2019	269,951	150,376
2018	127,313	43,839
2017	9,410	1,568
Prior to 2017	418	512
Revolving Loans	0	0
Revolving loans to term loans	5,938	4,347
Total gross loans	685,792	541,939
Construction \| Total classified and criticized
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	1,991
2020	1,975	14,508
2019	17,622	12,186
2018	2,967	615
2017	7,300	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	29,864	29,300
Construction \| Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	1,991
2020	1,975	14,508
2019	17,622	7,877
2018	0	0
2017	7,300	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	26,897	24,376
Construction \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	4,309
2018	2,967	615
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	2,967	4,924
Construction \| Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Construction \| Loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Construction \| Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
2021	114,736	88,777
2020	156,051	236,021
2019	252,329	138,190
2018	124,346	43,224
2017	2,110	1,568
Prior to 2017	418	512
Revolving Loans	0	0
Revolving loans to term loans	5,938	4,347
Total gross loans	655,928	512,639
Mortgage Portfolio Segment
Financing Receivable, Credit Quality Indicator [Line Items]
2021	832,991	1,251,149
2020	1,306,189	1,219,051
2019	1,196,997	885,763
2018	774,693	796,953
2017	686,558	575,553
Prior to 2017	2,073,800	1,941,138
Revolving Loans	95,424	72,067
Revolving loans to term loans	33,615	38,148
Total gross loans	7,000,267	6,779,822
Mortgage Portfolio Segment \| Total classified and criticized
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	2,155
2020	4,211	49,738
2019	50,093	70,825
2018	59,511	49,886
2017	43,389	21,091
Prior to 2017	108,521	118,099
Revolving Loans	2,019	0
Revolving loans to term loans	0	1,333
Total gross loans	267,744	313,127
Mortgage Portfolio Segment \| Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	1,991
2020	3,772	44,458
2019	48,916	61,160
2018	28,757	25,955
2017	34,672	8,722
Prior to 2017	42,871	38,051
Revolving Loans	1,094	0
Revolving loans to term loans	0	1,333
Total gross loans	160,082	181,670
Mortgage Portfolio Segment \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	164
2020	439	5,280
2019	1,177	9,665
2018	30,754	23,931
2017	8,717	12,369
Prior to 2017	65,650	80,048
Revolving Loans	926	0
Revolving loans to term loans	0	0
Total gross loans	107,663	131,457
Mortgage Portfolio Segment \| Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Mortgage Portfolio Segment \| Loss
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
Prior to 2017	0	0
Revolving Loans	0	0
Revolving loans to term loans	0	0
Total gross loans	0	0
Mortgage Portfolio Segment \| Pass/Watch
Financing Receivable, Credit Quality Indicator [Line Items]
2021	832,991	1,248,994
2020	1,301,978	1,169,313
2019	1,146,904	814,938
2018	715,182	747,067
2017	643,169	554,462
Prior to 2017	1,965,279	1,823,039
Revolving Loans	93,405	72,067
Revolving loans to term loans	33,615	36,815
Total gross loans	6,732,523	6,466,695
Mortgage Portfolio Segment \| Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Total gross loans	1,230,018	1,294,702
Mortgage Portfolio Segment \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total gross loans	3,704,684	3,458,666
Mortgage Portfolio Segment \| Multi-Family
Financing Receivable, Credit Quality Indicator [Line Items]
Total gross loans	1,379,773	1,484,515
Mortgage Portfolio Segment \| Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total gross loans	685,792	541,939
Commercial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2021	399,499	695,125
2020	231,599	221,019
2019	193,209	214,457
2018	179,646	222,458
2017	184,883	192,216
Prior to 2017	623,304	538,915
Revolving Loans	373,868	436,944
Revolving loans to term loans	48,011	46,335
Total gross loans	2,234,020	2,567,470
Commercial Loans \| Total classified and criticized
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,980	0
2020	2,907	13,619
2019	10,863	8,565
2018	9,287	43,390
2017	37,441	50,291
Prior to 2017	109,033	123,186
Revolving Loans	23,613	39,536
Revolving loans to term loans	5,999	5,635
Total gross loans	201,122	284,222
Commercial Loans \| Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,980	0
2020	2,818	6,295
2019	3,839	6,038

Loans Receivable and Allowance for Credit Losses (Summary of Loans Receivable by Credit Quality Risk Rating Indicator) (Detail) - USD ($)
$ in Thousands