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Debt Securities Available-for-Sale - Gross Unrealized Losses on Mortgage-Backed Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	$ (931)	$ (719)
Estimated fair value, less than 12 months	173,513	242,146
Unrealized losses, 12 months or more	(8)	(11)
Estimated fair value, 12 months or more	383	459
Unrealized losses, total	(939)	(730)
Estimated fair value, total	173,896	242,605
U.S. Government agency securities
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	(4)	(10)
Estimated fair value, less than 12 months	2,754	3,158
Unrealized losses, 12 months or more	0	0
Estimated fair value, 12 months or more	0	0
Unrealized losses, total	(4)	(10)
Estimated fair value, total	2,754	3,158
GSE | Pass-through Certificates
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	(378)	(233)
Estimated fair value, less than 12 months	31,540	28,419
Unrealized losses, 12 months or more	(8)	(11)
Estimated fair value, 12 months or more	383	459
Unrealized losses, total	(386)	(244)
Estimated fair value, total	31,923	28,878
GSE | Real estate mortgage investment conduits (REMICs)
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	(502)	(476)
Estimated fair value, less than 12 months	124,255	210,569
Unrealized losses, 12 months or more	0	0
Estimated fair value, 12 months or more	0	0
Unrealized losses, total	(502)	(476)
Estimated fair value, total	124,255	$ 210,569
Corporate bonds | Other debt securities
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	(47)
Estimated fair value, less than 12 months	14,964
Unrealized losses, 12 months or more	0
Estimated fair value, 12 months or more	0
Unrealized losses, total	(47)
Estimated fair value, total	$ 14,964

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