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Loans - Investment of Originated Loans Held-for-Investment by Loan Type and Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	$ 3,817,273	$ 3,823,238
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	3,800,581	3,804,720
Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	3,588,831	3,610,210
Commercial and industrial loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	209,580	191,481
Other loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	2,170	3,029
Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net		3,731,891
Pass | Commercial and industrial loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	206,295	189,372
Pass | Other loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	2,167	3,026
Special Mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net		24,145
Special Mention | Commercial and industrial loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	898	498
Special Mention | Other loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net		0
Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net		48,684
Substandard | Commercial and industrial loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	2,387	1,611
Substandard | Other loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	3	3
Multifamily | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	2,496,613	2,512,934
Multifamily | Pass | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	2,480,992	2,497,556
Multifamily | Special Mention | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	442	458
Multifamily | Substandard | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	15,179	14,920
Commercial mortgage | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	735,303	717,566
Commercial mortgage | Pass | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	698,500	667,568
Commercial mortgage | Special Mention | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	10,075	20,422
Commercial mortgage | Substandard | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	26,728	29,576
One-to-Four Family | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	193,976	212,222
One-to-Four Family | Pass | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	187,577	207,633
One-to-Four Family | Special Mention | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	2,866	2,456
One-to-Four Family | Substandard | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	3,533	2,133
Construction and land | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	63,125	74,351
Construction and land | Pass | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	62,018	74,351
Construction and land | Special Mention | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net		0
Construction and land | Substandard | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	1,107	0
Home equity and lines of credit | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	99,814	93,137
Home equity and lines of credit | Pass | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	99,141	92,385
Home equity and lines of credit | Special Mention | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	304	311
Home equity and lines of credit | Substandard | Real estate loans: | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans held-for-investment, net	$ 369	$ 441

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