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Loans - Troubled Debt Restructuring Loans (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) borrower loan	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) loan	Dec. 31, 2020 USD ($) contract	Dec. 31, 2020 USD ($) borrower
Financing Receivable, Modifications [Line Items]
Number of Relationships	2			4	3
Pre-Modification Outstanding Recorded Investment	$ 96,000		$ 731,000
Post-Modification Outstanding Recorded Investment	$ 96,000		731,000
Number of borrowers | borrower	2					3
Net loans held-for-investment	$ 3,767,644,000	$ 3,785,631,000	3,785,631,000	$ 3,785,631,000	$ 3,785,631,000	$ 3,785,631,000
Troubled debt restructurings	$ 9,000,000.0	$ 12,100,000	12,100,000	$ 12,100,000	$ 12,100,000	$ 12,100,000
Number of loans modified as TDR that subsequently defaulted | loan	0
Delinquent status classification term	90 days	90 days
COVID-19
Financing Receivable, Modifications [Line Items]
Number of Relationships | loan				4
Number of borrowers | borrower	2
Loan modification program, payment deferral period	90 days
Loan modification program, extension for payment deferral period	90 days
Net loans held-for-investment	$ 774,000
Residential
Financing Receivable, Modifications [Line Items]
Number of Relationships | loan	2
Pre-Modification Outstanding Recorded Investment	$ 96,000
Post-Modification Outstanding Recorded Investment	$ 96,000
One-to-four family residential mortgage
Financing Receivable, Modifications [Line Items]
Number of Relationships | contract					1
Pre-Modification Outstanding Recorded Investment			187,000
Post-Modification Outstanding Recorded Investment			187,000
Commercial Mortgage Backed Securities
Financing Receivable, Modifications [Line Items]
Number of Relationships	4				2
Pre-Modification Outstanding Recorded Investment			544,000
Post-Modification Outstanding Recorded Investment			544,000
Number of loans modified as TDR that subsequently defaulted | loan				2
Defaulted troubled debt restructuring loans			$ 462,500
Delinquent status classification term		90 days

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