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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 Held-to-maturity (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) Security | Dec. 31, 2016 USD ($) Security
Schedule Of Held To Maturity Securities [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 28 | 42
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 42,211 | $ 97,636
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (155) | (954)
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 13,865 |
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (181) |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Fair Value | 56,076 | 97,636
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (336) | $ (954)
Obligations of States, Municipalities, and Political Subdivisions |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 12 | 22
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 7,409 | $ 16,235
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (38) | (229)
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 1,548 |
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (44) |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Fair Value | 8,957 | 16,235
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (82) | $ (229)
Agency, Residential Mortgage-Backed Securities |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 13 | 15
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 24,344 | $ 52,156
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (107) | (283)
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 7,935 |
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (96) |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Fair Value | 32,279 | 52,156
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (203) | $ (283)
Non-Agency, Residential Mortgage-Backed Securities |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Number of Securities | Security | 3 | 5
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value | $ 10,458 | $ 29,245
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses | (10) | (442)
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value | 4,382 |
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses | (41) |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Fair Value | 14,840 | 29,245
Held-to-maturity Securities, Continuous Unrealized Loss Position, Total Unrealized Losses | $ (51) | $ (442)

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- Definition This item represents the fair value of securities categorized as held-to-maturity which are in an unrealized loss position. + 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)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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