Debt Securities Available-for-Sale - Gross Unrealized Losses on Mortgage-Backed Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	$ 302	$ 2,376
Estimated Fair value, less than 12 months	106,717	302,921
Unrealized losses, 12 months or more	7,812	11,361
Estimated Fair value, 12 months or more	303,061	307,354
Unrealized losses, total	8,114	13,737
Estimated fair value, total	409,778	610,275
GSE \| Pass-through Certificates
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	170	404
Estimated Fair value, less than 12 months	34,164	82,781
Unrealized losses, 12 months or more	2,057	3,138
Estimated Fair value, 12 months or more	96,411	100,109
Unrealized losses, total	2,227	3,542
Estimated fair value, total	130,575	182,890
GSE \| Real estate mortgage investment conduits (REMICs)
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	8	269
Estimated Fair value, less than 12 months	19,136	46,921
Unrealized losses, 12 months or more	5,464	7,710
Estimated Fair value, 12 months or more	170,787	181,512
Unrealized losses, total	5,472	7,979
Estimated fair value, total	189,923	228,433
Non-GSE \| Real estate mortgage investment conduits (REMICs)
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	1	1
Estimated Fair value, 12 months or more	57	58
Unrealized losses, total	1	1
Estimated fair value, total	57	58
Corporate bonds \| Other debt obligations
Debt Securities, Available-for-sale [Line Items]
Unrealized losses, less than 12 months	124	1,703
Estimated Fair value, less than 12 months	53,417	173,219
Unrealized losses, 12 months or more	290	512
Estimated Fair value, 12 months or more	35,806	25,675
Unrealized losses, total	414	2,215
Estimated fair value, total	$ 89,223	$ 198,894

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on 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 12 months or longer.

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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), in unrealized loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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