Loans Receivable and Allowance for Credit Losses (Summary of Loans Receivable by Credit Quality Risk Rating Indicator) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
2021	$ 468,843
2020	1,991,107
2019	1,574,207
2018	1,152,030
2017 and prior	4,633,456
Total gross loans	9,819,643	$ 9,839,858
Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	414
2020	4,318
2019	73,074
2018	83,889
2017 and prior	419,475
Criticized and classified loans, gross	132,000
Total gross loans	581,170	605,963
Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	23
2020	2,331
2019	56,658
2018	65,953
2017 and prior	187,375
Total gross loans	312,340	340,617
Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	391
2020	1,987
2019	16,416
2018	17,936
2017 and prior	232,080
Total gross loans	268,810	265,294
Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	20
Total gross loans	20	52
Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	468,429
2020	1,986,789
2019	1,501,133
2018	1,068,141
2017 and prior	4,213,981
Total gross loans	9,238,473	9,233,895
Mortgage Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
2021	207,437
2020	1,354,272
2019	1,262,944
2018	868,673
2017 and prior	3,251,961
Total gross loans	6,945,287	6,779,822
Mortgage Portfolio Segment | Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	2,149
2019	54,038
2018	73,623
2017 and prior	206,775
Total gross loans	336,585	313,126
Mortgage Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	1,986
2019	47,839
2018	62,375
2017 and prior	83,992
Total gross loans	196,192	181,670
Mortgage Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	163
2019	6,199
2018	11,248
2017 and prior	122,783
Total gross loans	140,393	131,456
Mortgage Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	207,437
2020	1,352,123
2019	1,208,906
2018	795,050
2017 and prior	3,045,186
Total gross loans	6,608,702	6,466,696
Mortgage Portfolio Segment | Residential
Financing Receivable, Recorded Investment [Line Items]
2021	82,831
2020	262,195
2019	144,385
2018	84,489
2017 and prior	703,476
Total gross loans	1,277,376	1,294,702
Mortgage Portfolio Segment | Residential | Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	163
2019	4,434
2018	3,169
2017 and prior	21,497
Total gross loans	29,263	29,533
Mortgage Portfolio Segment | Residential | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	661
2018	2,425
2017 and prior	2,761
Total gross loans	5,847	2,882
Mortgage Portfolio Segment | Residential | Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	163
2019	3,773
2018	744
2017 and prior	18,736
Total gross loans	23,416	26,651
Mortgage Portfolio Segment | Residential | Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Residential | Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Residential | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	82,831
2020	262,032
2019	139,951
2018	81,320
2017 and prior	681,979
Total gross loans	1,248,113	1,265,169
Mortgage Portfolio Segment | Commercial
Financing Receivable, Recorded Investment [Line Items]
2021	78,552
2020	670,040
2019	664,820
2018	430,288
2017 and prior	1,750,312
Total gross loans	3,594,012	3,458,666
Mortgage Portfolio Segment | Commercial | Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	32,736
2018	45,208
2017 and prior	160,796
Total gross loans	238,740	222,944
Mortgage Portfolio Segment | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	30,310
2018	39,825
2017 and prior	58,916
Total gross loans	129,051	124,631
Mortgage Portfolio Segment | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	2,426
2018	5,383
2017 and prior	101,880
Total gross loans	109,689	98,313
Mortgage Portfolio Segment | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Commercial | Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Commercial | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	78,552
2020	670,040
2019	632,084
2018	385,080
2017 and prior	1,589,516
Total gross loans	3,355,272	3,235,722
Mortgage Portfolio Segment | Multi-Family
Financing Receivable, Recorded Investment [Line Items]
2021	31,141
2020	296,124
2019	178,327
2018	203,468
2017 and prior	749,133
Total gross loans	1,458,193	1,484,515
Mortgage Portfolio Segment | Multi-Family | Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	679
2018	20,125
2017 and prior	16,633
Total gross loans	37,437	31,349
Mortgage Portfolio Segment | Multi-Family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	679
2018	20,125
2017 and prior	15,081
Total gross loans	35,885	29,781
Mortgage Portfolio Segment | Multi-Family | Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	1,552
Total gross loans	1,552	1,568
Mortgage Portfolio Segment | Multi-Family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Multi-Family | Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Multi-Family | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	31,141
2020	296,124
2019	177,648
2018	183,343
2017 and prior	732,500
Total gross loans	1,420,756	1,453,166
Mortgage Portfolio Segment | Construction
Financing Receivable, Recorded Investment [Line Items]
2021	14,913
2020	125,913
2019	275,412
2018	150,428
2017 and prior	49,040
Total gross loans	615,706	541,939
Mortgage Portfolio Segment | Construction | Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	1,986
2019	16,189
2018	5,121
2017 and prior	7,849
Total gross loans	31,145	29,300
Mortgage Portfolio Segment | Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	1,986
2019	16,189
2018	0
2017 and prior	7,234
Total gross loans	25,409	24,376
Mortgage Portfolio Segment | Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	5,121
2017 and prior	615
Total gross loans	5,736	4,924
Mortgage Portfolio Segment | Construction | Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Construction | Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Mortgage Portfolio Segment | Construction | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	14,913
2020	123,927
2019	259,223
2018	145,307
2017 and prior	41,191
Total gross loans	584,561	512,639
Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
2021	252,459
2020	597,728
2019	264,747
2018	239,109
2017 and prior	1,156,665
Total gross loans	2,510,708	2,567,470
Commercial Loans | Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	414
2020	2,169
2019	18,675
2018	10,146
2017 and prior	208,816
Total gross loans	240,220	284,224
Commercial Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	23
2020	345
2019	8,819
2018	3,578
2017 and prior	102,854
Total gross loans	115,619	157,080
Commercial Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	391
2020	1,824
2019	9,856
2018	6,568
2017 and prior	105,942
Total gross loans	124,581	127,092
Commercial Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	20
Total gross loans	20	52
Commercial Loans | Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Commercial Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	252,045
2020	595,559
2019	246,072
2018	228,963
2017 and prior	947,849
Total gross loans	2,270,488	2,283,246
Consumer Loans
Financing Receivable, Recorded Investment [Line Items]
2021	8,947
2020	39,107
2019	46,516
2018	44,248
2017 and prior	224,830
Total gross loans	363,648	492,566
Consumer Loans | Criticized
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	361
2018	120
2017 and prior	3,884
Total gross loans	4,365	8,613
Consumer Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	529
Total gross loans	529	1,867
Consumer Loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	361
2018	120
2017 and prior	3,355
Total gross loans	3,836	6,746
Consumer Loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Consumer Loans | Loss
Financing Receivable, Recorded Investment [Line Items]
2021	0
2020	0
2019	0
2018	0
2017 and prior	0
Total gross loans	0	0
Consumer Loans | Pass/Watch
Financing Receivable, Recorded Investment [Line Items]
2021	8,947
2020	39,107
2019	46,155
2018	44,128
2017 and prior	220,946
Total gross loans	$ 359,283	$ 483,953