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Debt Securities Available-for-Sale - Comparative Summary of Mortgage-Backed Securities and Other Securities Available-for-Sale) (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | $ 898,434 | $ 820,801
Gross unrealized gains | 3,952 | 967
Gross unrealized losses | 8,114 | 13,737
Debt securities available-for-sale | 894,272 | 808,031
Real estate mortgage investment conduits (REMICs) |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 672,565 | 575,639
Gross unrealized gains | 3,221 | 892
Gross unrealized losses | 7,700 | 11,522
Debt securities available-for-sale | 668,086 | 565,009
Other debt obligations |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 225,869 | 245,162
Gross unrealized gains | 731 | 75
Gross unrealized losses | 414 | 2,215
Debt securities available-for-sale | 226,186 | 243,022
GSE | Pass-through Certificates |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 404,108 | 317,530
Gross unrealized gains | 2,656 | 800
Gross unrealized losses | 2,227 | 3,542
Debt securities available-for-sale | 404,537 | 314,788
GSE | Real estate mortgage investment conduits (REMICs) |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 268,399 | 258,050
Gross unrealized gains | 565 | 92
Gross unrealized losses | 5,472 | 7,979
Debt securities available-for-sale | 263,492 | 250,163
Non-GSE | Real estate mortgage investment conduits (REMICs) |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 58 | 59
Gross unrealized gains | 0 | 0
Gross unrealized losses | 1 | 1
Debt securities available-for-sale | 57 | 58
Municipal bonds | Other debt obligations |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 270 | 270
Gross unrealized gains | 4 | 3
Gross unrealized losses | 0 | 0
Debt securities available-for-sale | 274 | 273
Corporate bonds | Other debt obligations |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized cost | 225,599 | 244,892
Gross unrealized gains | 727 | 72
Gross unrealized losses | 414 | 2,215
Debt securities available-for-sale | $ 225,912 | $ 242,749

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- Definition 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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- Definition 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 -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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