Debt Securities Available-for-Sale - Narrative (Details)	3 Months Ended
Mar. 31, 2020 USD ($) security	Mar. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, restricted \| $	$ 732,000,000.0
Proceeds from sale of debt securities available-for-sale \| $	0	$ 29,163,000
Debt securities, available-for-sale, realized gain \| $	0	155,000
Debt securities, available-for-sale, realized loss \| $	13,000	0
Debt securities, trading, realized gain (loss) \| $	2,000,000.0	1,100,000
Other-than-temporary impairment loss, debt securities, available for sale, recognized in earnings \| $	$ 0	$ 0
Real Estate Mortgage Investment Conduits (REMICs) \| GSE \| Pass Through
Debt Securities, Available-for-sale [Line Items]
Number of debt securities, unrealized loss position longer than 12 months	12
Real Estate Mortgage Investment Conduits (REMICs) \| GSE \| Non Pass Through
Debt Securities, Available-for-sale [Line Items]
Number of debt securities, unrealized loss position longer than 12 months	4
Number of debt securities, unrealized loss position less than 12 months	19
Real Estate Mortgage Investment Conduits (REMICs) \| Non-GSE
Debt Securities, Available-for-sale [Line Items]
Number of debt securities, unrealized loss position longer than 12 months	1
Real Estate Mortgage Investment Conduits (REMICs) \| Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Number of debt securities, unrealized loss position less than 12 months	2
Real Estate Mortgage Investment Conduits (REMICs) \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Number of debt securities, unrealized loss position less than 12 months	11
Pass-through Certificates \| GSE \| Pass Through
Debt Securities, Available-for-sale [Line Items]
Number of debt securities, unrealized loss position less than 12 months	2

Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455

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

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Amount of realized gain on 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
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Amount of restricted 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=118954083&loc=SL6284422-111562

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Amount of cash inflow from sale 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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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