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Investment Securities - Schedule Of Investments Within The Available For Sale Portfolio That Had Unrealized Losses (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value | $ 2,677,574 | $ 2,514,856
Less than 12 months, Unrealized Losses | (83,377) | (12,243)
12 months or longer, Fair Value | 1,696,331 | 1,164,073
12 months or longer, Unrealized Losses | (97,300) | (35,674)
Total Fair Value | 4,373,905 | 3,678,929
Total Unrealized Losses | (180,677) | (47,917)
U.S. treasuries |  |
Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value | 0 | 99
Less than 12 months, Unrealized Losses | 0 | (1)
12 months or longer, Fair Value | 98 | 0
12 months or longer, Unrealized Losses | (2) | 0
Total Fair Value | 98 | 99
Total Unrealized Losses | (2) | (1)
Government agency issued MBS |  |
Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value | 1,500,317 | 1,455,476
Less than 12 months, Unrealized Losses | (52,607) | (4,738)
12 months or longer, Fair Value | 732,470 | 331,900
12 months or longer, Unrealized Losses | (39,604) | (8,866)
Total Fair Value | 2,232,787 | 1,787,376
Total Unrealized Losses | (92,211) | (13,604)
Government agency issued CMO |  |
Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value | 1,000,444 | 1,043,987
Less than 12 months, Unrealized Losses | (28,664) | (7,464)
12 months or longer, Fair Value | 963,763 | 832,173
12 months or longer, Unrealized Losses | (57,694) | (26,808)
Total Fair Value | 1,964,207 | 1,876,160
Total Unrealized Losses | (86,358) | (34,272)
Other U.S. government agencies |  |
Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value | 113,088 |
Less than 12 months, Unrealized Losses | (965) |
12 months or longer, Fair Value | 0 |
12 months or longer, Unrealized Losses | 0 |
Total Fair Value | 113,088 |
Total Unrealized Losses | (965) |
Corporates and other debt |  |
Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value | 40,024 |
Less than 12 months, Unrealized Losses | (691) |
12 months or longer, Fair Value | 0 |
12 months or longer, Unrealized Losses | 0 |
Total Fair Value | 40,024 |
Total Unrealized Losses | (691) |
States and municipalities |  |
Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value | 23,701 |
Less than 12 months, Unrealized Losses | (450) |
12 months or longer, Fair Value | 0 |
12 months or longer, Unrealized Losses | 0 |
Total Fair Value | 23,701 |
Total Unrealized Losses | $ (450) |
Corporates and other debt |  |
Schedule of Investments [Line Items] |  |
Less than 12 months, Fair Value |  | 15,294
Less than 12 months, Unrealized Losses |  | (40)
12 months or longer, Fair Value |  | 0
12 months or longer, Unrealized Losses |  | 0
Total Fair Value |  | 15,294
Total Unrealized Losses |  | $ (40)

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- Definition 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. + References 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 + Details
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