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AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Schedule of Available-for-sale Securities |  |
Amortized Cost | $ 3,783,829 | $ 2,619,307
Gross Unrealized Gains | 11,744 | 21,278
Gross Unrealized Losses | (22,347) | (13,968)
Available-for-sale investment securities, at fair value | 3,773,226 | 2,626,617
U.S. Treasury securities |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 1,002,874 | 873,101
Gross Unrealized Gains | 33 | 1,971
Gross Unrealized Losses | (4,392) | (1,637)
Available-for-sale investment securities, at fair value | 998,515 | 873,435
U.S. government agency and U.S. government sponsored enterprise debt securities |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 771,288 | 311,927
Gross Unrealized Gains | 555 | 490
Gross Unrealized Losses | (2,994) | (1,393)
Available-for-sale investment securities, at fair value | 768,849 | 311,024
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 354,418 | 140,957
Gross Unrealized Gains | 268 | 1,056
Gross Unrealized Losses | (3,024) | (593)
Available-for-sale investment securities, at fair value | 351,662 | 141,420
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 996,255 | 785,412
Gross Unrealized Gains | 7,542 | 9,754
Gross Unrealized Losses | (6,401) | (4,078)
Available-for-sale investment securities, at fair value | 997,396 | 791,088
Municipal securities |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 173,785 | 245,408
Gross Unrealized Gains | 2,657 | 6,202
Gross Unrealized Losses | (793) | (1,162)
Available-for-sale investment securities, at fair value | 175,649 | 250,448
Other residential mortgage-backed securities: | Investment grade |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 62,133 | 52,694
Gross Unrealized Gains | 433 | 1,359
Gross Unrealized Losses | (173) | (135)
Available-for-sale investment securities, at fair value | 62,393 | 53,918
Other commercial mortgage-backed securities: | Investment grade |  |
Schedule of Available-for-sale 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 Securities |  |
Amortized Cost | 366,921 | 116,236
Gross Unrealized Gains | 132 | 0
Gross Unrealized Losses | (2,340) | (1,054)
Available-for-sale investment securities, at fair value | 364,713 | 115,182
Corporate debt securities: | Non-investment grade |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 11,491 | 17,881
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (1,849) | (3,200)
Available-for-sale investment securities, at fair value | 9,642 | 14,681
Other securities |  |
Schedule of Available-for-sale Securities |  |
Amortized Cost | 44,664 | 41,691
Gross Unrealized Gains | 124 | 393
Gross Unrealized Losses | (381) | (716)
Available-for-sale investment securities, at fair value | $ 44,407 | $ 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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