Debt Securities Available-for-Sale - Comparative Summary of Mortgage-Backed Securities and Other Securities Available-for-Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 1,046,738	$ 1,131,970
Gross unrealized gains	17,096	9,374
Gross unrealized losses	2,391	2,992
Debt securities available-for-sale	1,061,443	1,138,352
Real estate mortgage investment conduits (REMICs)
Debt Securities, Available-for-sale [Line Items]
Amortized cost	918,817	967,949
Gross unrealized gains	16,676	8,157
Gross unrealized losses	995	2,979
Debt securities available-for-sale	934,498	973,127
Other debt obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	127,921	164,021
Gross unrealized gains	420	1,217
Gross unrealized losses	1,396	13
Debt securities available-for-sale	126,945	165,225
GSE \| Pass-through Certificates
Debt Securities, Available-for-sale [Line Items]
Amortized cost	300,610	324,080
Gross unrealized gains	10,340	6,081
Gross unrealized losses	81	754
Debt securities available-for-sale	310,869	329,407
GSE \| Real estate mortgage investment conduits (REMICs)
Debt Securities, Available-for-sale [Line Items]
Amortized cost	618,156	643,816
Gross unrealized gains	6,336	2,076
Gross unrealized losses	912	2,225
Debt securities available-for-sale	623,580	643,667
Non-GSE \| Real estate mortgage investment conduits (REMICs)
Debt Securities, Available-for-sale [Line Items]
Amortized cost	51	53
Gross unrealized gains	0	0
Gross unrealized losses	2	0
Debt securities available-for-sale	49	53
Municipal bonds \| Other debt obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	278	296
Gross unrealized gains	1	3
Gross unrealized losses	0	0
Debt securities available-for-sale	279	299
Corporate bonds \| Other debt obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	127,643	163,725
Gross unrealized gains	419	1,214
Gross unrealized losses	1,396	13
Debt securities available-for-sale	$ 126,666	$ 164,926

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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