Loans Receivable and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Allowance for credit losses:
Total	$ 53,456	$ 52,873	$ 52,803	$ 50,583	$ 47,162	$ 62,689
Total loans:
Total	7,725,645		7,641,593
Real estate loans | One-to-four family
Allowance for credit losses:
Total	11,026	12,789	11,802	10,836	8,814	8,798
Total loans:
Total	2,791,201		2,862,342
Real estate loans | Multifamily
Allowance for credit losses:
Total	9,392	8,145	7,877	10,932	11,203	7,741
Total loans:
Total	1,376,999		1,239,207
Real estate loans | Commercial real estate
Allowance for credit losses:
Total	16,212	16,257	18,111	14,480	13,513	16,114
Total loans:
Total	2,399,479		2,426,510
Real estate loans | Construction
Allowance for credit losses:
Total	6,935	6,739	6,425	5,570	4,974	8,943
Total loans:
Total	380,028		337,593
Commercial business loans
Allowance for credit losses:
Total	7,690	7,320	6,897	7,284	7,143	20,214
Total loans:
Total	505,933		497,965
Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	2,193	1,614	1,681	1,471	1,507	873
Total loans:
Total	269,453		274,551
Consumer loans | Other consumer loans
Allowance for credit losses:
Total	8	$ 9	10	$ 10	$ 8	$ 6
Total loans:
Total	2,552		3,425
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Individually analyzed loans	622		339
Collectively analyzed loans	52,752		52,381
Total loans:
Individually analyzed loans	25,912		23,220
Collectively analyzed loans	7,683,626		7,601,314
Total	7,709,538		7,624,534
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Individually analyzed loans	209		201
Collectively analyzed loans	10,813		11,591
Total loans:
Individually analyzed loans	4,691		4,164
Collectively analyzed loans	2,784,578		2,856,020
Total	2,789,269		2,860,184
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Allowance for credit losses:
Individually analyzed loans	2		3
Collectively analyzed loans	9,390		7,874
Total loans:
Individually analyzed loans	420		457
Collectively analyzed loans	1,376,579		1,238,750
Total	1,376,999		1,239,207
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Allowance for credit losses:
Individually analyzed loans	309		99
Collectively analyzed loans	15,855		17,961
Total loans:
Individually analyzed loans	16,538		16,729
Collectively analyzed loans	2,370,358		2,396,665
Total	2,386,896		2,413,394
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Individually analyzed loans	0		0
Collectively analyzed loans	6,925		6,415
Total loans:
Individually analyzed loans	0		0
Collectively analyzed loans	378,988		336,553
Total	378,988		336,553
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Individually analyzed loans	74		10
Collectively analyzed loans	7,596		6,876
Total loans:
Individually analyzed loans	3,622		1,173
Collectively analyzed loans	501,902		496,296
Total	505,524		497,469
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Individually analyzed loans	28		26
Collectively analyzed loans	2,165		1,654
Total loans:
Individually analyzed loans	641		697
Collectively analyzed loans	268,669		273,605
Total	269,310		274,302
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for credit losses:
Individually analyzed loans	0		0
Collectively analyzed loans	8		10
Total loans:
Individually analyzed loans	0		0
Collectively analyzed loans	2,552		3,425
Total	2,552		3,425
Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Total	82		83
Total loans:
Total	16,107		17,059
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Total	4		10
Total loans:
Total	1,932		2,158
Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Allowance for credit losses:
Total	0		0
Total loans:
Total	0		0
Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Allowance for credit losses:
Total	48		51
Total loans:
Total	12,583		13,116
Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Total	10		10
Total loans:
Total	1,040		1,040
Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Total	20		11
Total loans:
Total	409		496
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	0		1
Total loans:
Total	143		249
Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for credit losses:
Total	0		0
Total loans:
Total	$ 0		$ 0