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AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands | Sep. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | $ 2,937,313 | $ 2,619,307
Gross Unrealized Gains | 23,056 | 21,278
Gross Unrealized Losses | (8,092) | (13,968)
Available-for-sale investment securities, at fair value | 2,952,277 | 2,626,617
U.S. Treasury securities |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 750,032 | 873,101
Gross Unrealized Gains | 2,581 | 1,971
Gross Unrealized Losses | (8) | (1,637)
Available-for-sale investment securities, at fair value | 752,605 | 873,435
U.S. government agency and U.S. government sponsored enterprise debt securities |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 701,919 | 311,927
Gross Unrealized Gains | 1,544 | 490
Gross Unrealized Losses | (1,619) | (1,393)
Available-for-sale investment securities, at fair value | 701,844 | 311,024
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 271,171 | 140,957
Gross Unrealized Gains | 2,584 | 1,056
Gross Unrealized Losses | (405) | (593)
Available-for-sale investment securities, at fair value | 273,350 | 141,420
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 746,632 | 785,412
Gross Unrealized Gains | 10,081 | 9,754
Gross Unrealized Losses | (1,815) | (4,078)
Available-for-sale investment securities, at fair value | 754,898 | 791,088
Municipal securities |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 203,832 | 245,408
Gross Unrealized Gains | 4,604 | 6,202
Gross Unrealized Losses | (1,611) | (1,162)
Available-for-sale investment securities, at fair value | 206,825 | 250,448
Other residential mortgage-backed securities | Investment grade |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 65,706 | 52,694
Gross Unrealized Gains | 947 | 1,359
Gross Unrealized Losses | (116) | (135)
Available-for-sale investment securities, at fair value | 66,537 | 53,918
Other commercial mortgage-backed securities | Investment grade |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost |  | 34,000
Gross Unrealized Gains |  | 53
Gross Unrealized Losses |  | 0
Available-for-sale investment securities, at fair value |  | 34,053
Corporate debt securities | Investment grade |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 142,216 | 116,236
Gross Unrealized Gains | 22 | 0
Gross Unrealized Losses | (1,112) | (1,054)
Available-for-sale investment securities, at fair value | 141,126 | 115,182
Corporate debt securities | Non-investment grade |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 11,525 | 17,881
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (1,001) | (3,200)
Available-for-sale investment securities, at fair value | 10,524 | 14,681
Other securities |  |
Schedule of Available-for-sale Investment Securities |  |
Amortized Cost | 44,280 | 41,691
Gross Unrealized Gains | 693 | 393
Gross Unrealized Losses | (405) | (716)
Available-for-sale investment securities, at fair value | $ 44,568 | $ 41,368

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 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=49167202&loc=d3e26610-111562 + Details
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