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Trading Securities (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017 | Jun. 30, 2017
--- | --- | --- | ---
Schedule of Trading Securities [Line Items] |  |  |
Trading Securities, Fair Value | $ 1,909,615 | $ 462,676 | $ 441,414
Trading Securities, Net Unrealized Gain (Loss) | 2,446 | (448) | (986)
Trading Securities Pledged as Collateral | 889,000 | 0 | 0
U.S. government agency debentures |  |  |
Schedule of Trading Securities [Line Items] |  |  |
Trading Securities, Fair Value | 28,750 | 21,196 | 20,954
Trading Securities, Net Unrealized Gain (Loss) | 10 | 8 | (9)
U.S. government agency residential mortgage-backed securities |  |  |
Schedule of Trading Securities [Line Items] |  |  |
Trading Securities, Fair Value | 1,605,001 | 392,673 | 365,171
Trading Securities, Net Unrealized Gain (Loss) | 1,923 | (517) | (1,032)
Municipal and other tax-exempt securities |  |  |
Schedule of Trading Securities [Line Items] |  |  |
Trading Securities, Fair Value | 70,606 | 13,559 | 45,444
Trading Securities, Net Unrealized Gain (Loss) | 231 | 83 | 230
Asset-backed securities |  |  |
Schedule of Trading Securities [Line Items] |  |  |
Trading Securities, Fair Value | 193,271 | 23,885 | 0
Trading Securities, Net Unrealized Gain (Loss) | 250 | (26) | 0
Other trading securities |  |  |
Schedule of Trading Securities [Line Items] |  |  |
Trading Securities, Fair Value | 11,987 | 11,363 | 9,845
Trading Securities, Net Unrealized Gain (Loss) | $ 32 | $ 4 | $ (175)

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- Definition Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 + Details
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