Debt Securities Available-for-Sale - Gross Unrealized Losses on Mortgage-Backed Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	$ 112	$ 975
Estimated fair value, less than 12 months	31,892	201,038
Unrealized losses, 12 months or more	90	2,017
Estimated fair value, 12 months or more	13,871	125,378
Unrealized losses, total	202	2,992
Estimated fair value, total	45,763	326,416
GSE \| Pass-through Certificates
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	0	25
Estimated fair value, less than 12 months	0	3,404
Unrealized losses, 12 months or more	75	729
Estimated fair value, 12 months or more	543	55,184
Unrealized losses, total	75	754
Estimated fair value, total	543	58,588
GSE \| Real estate mortgage investment conduits (REMICs)
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	112	950
Estimated fair value, less than 12 months	31,767	197,634
Unrealized losses, 12 months or more	14	1,275
Estimated fair value, 12 months or more	13,281	54,555
Unrealized losses, total	126	2,225
Estimated fair value, total	45,048	252,189
Non-GSE \| Real estate mortgage investment conduits (REMICs)
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	0	0
Estimated fair value, less than 12 months	0	0
Unrealized losses, 12 months or more	1	0
Estimated fair value, 12 months or more	47	53
Unrealized losses, total	1	0
Estimated fair value, total	47	53
Municipal bonds \| Other debt obligations
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	0
Estimated fair value, less than 12 months	125
Unrealized losses, 12 months or more	0
Estimated fair value, 12 months or more	0
Unrealized losses, total	0
Estimated fair value, total	$ 125
Corporate bonds \| Other debt obligations
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months		0
Estimated fair value, less than 12 months		0
Unrealized losses, 12 months or more		13
Estimated fair value, 12 months or more		15,586
Unrealized losses, total		13
Estimated fair value, total		$ 15,586

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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