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Securities - Summary of Gross Unrealized Losses and Fair Values, Aggregated by Investment Category and Length of Individual Securities Continuous Unrealized Loss Position Available-for-sale (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) Security | Dec. 31, 2016 USD ($) Security
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 101 | 88
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 39,896 | $ 568,131
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (407) | (12,893)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 455,688 | 14,719
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (12,010) | (297)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 495,584 | 582,850
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (12,417) | $ (13,190)
U.S. Treasury Notes |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 5 | 3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 4,998 | $ 9,918
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (2) | (79)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 9,865 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (134) |
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 14,863 | 9,918
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (136) | $ (79)
U.S. Government Agencies |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 9 | 10
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 992 | $ 58,857
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (7) | (1,323)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 51,966 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (1,283) |
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 52,958 | 58,857
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (1,290) | $ (1,323)
Obligations of States, Municipalities, and Political Subdivisions |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 29 | 14
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 16,059 | $ 7,799
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (137) | (259)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 4,453 | 115
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (198) | (13)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 20,512 | 7,914
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (335) | $ (272)
Agency, Residential Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 41 | 41
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 15,441 | $ 364,713
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (181) | (8,483)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 292,016 | 3,447
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (7,465) | (157)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 307,457 | 368,160
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (7,646) | $ (8,640)
Non-Agency, Residential Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 1 | 2
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value |  | $ 19,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses |  | (174)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | $ 4,565 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (75) |
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 4,565 | 19,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (75) | $ (174)
Agency, Commercial Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 7 | 8
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value |  | $ 70,762
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses |  | (1,488)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | $ 57,442 | 6,641
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (1,966) | (63)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 57,442 | 77,403
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (1,966) | $ (1,551)
Non-Agency, Commercial Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 5 | 5
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value |  | $ 31,052
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses |  | (1,009)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | $ 30,971 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (792) |
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 30,971 | 31,052
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (792) | $ (1,009)
Corporate Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 3 | 4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 2,406 | $ 5,097
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (80) | (78)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 2,489 | 2,522
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (24) | (8)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 4,895 | 7,619
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (104) | $ (86)
Other Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 1 | 1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | $ 1,921 | $ 1,994
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (73) | (56)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 1,921 | 1,994
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (73) | $ (56)

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- Definition Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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