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Investment Securities - Other Than Temporarily Impaired Debt Securities (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) security | Dec. 31, 2016 USD ($) security | Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items] |  |  |
Number of securities considered other than temporarily impaired | security | 0 |  |
Number of investment securities in unrealized loss positions | security | 198 | 134 |
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Held-to-maturity, Less than 12 continuous months, Fair value | $ 31,051 | $ 9,130 |
Held-to-maturity, Less than 12 continuous months, Unrealized loss | (205) | (161) |
Held-to-maturity, Greater than 12 continuous months, Fair value | 60,669 | 0 |
Held-to-maturity, Greater than 12 continuous months, Unrealized loss | (414) | 0 |
Held-to-maturity, Total securities in a loss position, Fair value | 91,720 | 9,130 |
Held-to-maturity, Total securities in a loss position, Unrealized loss | (619) | (161) |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | 212,675 | 284,314 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (1,465) | (6,197) |
Available-for-sale, Greater than 12 continuous months, Fair value | 40,478 | 9,946 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | (927) | (52) |
Available-for-sale, Total securities in a loss position, Fair value | 253,153 | 294,260 |
Available-for-sale, Total securities in a loss position, Unrealized loss | (2,392) | (6,249) |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Total temporarily impaired securities, Less than 12 continuous months, Fair value | 243,726 | 293,444 |
Total temporarily impaired securities, Less than 12 continuous months, Unrealized loss | (1,670) | (6,358) |
Total temporarily impaired securities, Greater than 12 continuous months, Fair value | 101,147 | 9,946 |
Total temporarily impaired securities, Greater than 12 continuous months, Unrealized loss | (1,341) | (52) |
Total temporarily impaired securities, Total securities in a loss position, Fair value | 344,873 | 303,390 |
Total temporarily impaired securities, Total securities in a loss position, Unrealized loss | $ (3,011) | (6,410) |
Number of securities in continuous loss position for more than 12 months | security | 55 |  |
Number of securities in continuous loss position for less than 12 months | security | 143 |  |
Net loss on sale of available for sale securities sold | $ 231 | 64 | $ 1
MBS pass-through securities |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | 32,189 | 161,409 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (121) | (3,570) |
Available-for-sale, Greater than 12 continuous months, Fair value | 15,325 | 0 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | (302) | 0 |
Available-for-sale, Total securities in a loss position, Fair value | 47,514 | 161,409 |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (423) | (3,570) |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for more than 12 months | security | 16 |  |
Number of securities in continuous loss position for less than 12 months | security | 16 |  |
SBA-backed securities |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | $ 11,028 | 607 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (53) | (7) |
Available-for-sale, Greater than 12 continuous months, Fair value | 165 | 0 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | (2) | 0 |
Available-for-sale, Total securities in a loss position, Fair value | 11,193 | 607 |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (55) | (7) |
Collateralized Mortgage Obligations |  |  |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for less than 12 months | security | 34 |  |
CMOs issued by FNMA |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | $ 26,401 | 9,498 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (171) | (109) |
Available-for-sale, Greater than 12 continuous months, Fair value | 5,440 | 0 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | (77) | 0 |
Available-for-sale, Total securities in a loss position, Fair value | 31,841 | 9,498 |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (248) | (109) |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for more than 12 months | security | 3 |  |
CMOs issued by FHLMC |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | $ 69,276 | 31,545 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (628) | (731) |
Available-for-sale, Greater than 12 continuous months, Fair value | 0 | 0 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | 0 | 0 |
Available-for-sale, Total securities in a loss position, Fair value | 69,276 | 31,545 |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (628) | (731) |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for more than 12 months | security | 4 |  |
CMOs issued by GNMA |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | $ 14,230 | 1,583 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (194) | (1) |
Available-for-sale, Greater than 12 continuous months, Fair value | 0 | 0 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | 0 | 0 |
Available-for-sale, Total securities in a loss position, Fair value | 14,230 | 1,583 |
Available-for-sale, Total securities in a loss position, Unrealized loss | (194) | (1) |
Debentures of government- sponsored agencies |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | 2,984 | 19,951 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (5) | (38) |
Available-for-sale, Greater than 12 continuous months, Fair value | 0 | 9,946 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | 0 | (52) |
Available-for-sale, Total securities in a loss position, Fair value | 2,984 | 29,897 |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (5) | (90) |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for less than 12 months | security | 5 |  |
Obligations of state and political subdivisions |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | $ 52,197 | 59,567 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (288) | (1,740) |
Available-for-sale, Greater than 12 continuous months, Fair value | 19,548 | 0 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | (546) | 0 |
Available-for-sale, Total securities in a loss position, Fair value | 71,745 | 59,567 |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (834) | (1,740) |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for more than 12 months | security | 32 |  |
Number of securities in continuous loss position for less than 12 months | security | 81 |  |
Corporate bonds |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | $ 3,060 | 154 |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (3) | (1) |
Available-for-sale, Greater than 12 continuous months, Fair value |  | 0 |
Available-for-sale, Greater than 12 continuous months, Unrealized loss |  | 0 |
Available-for-sale, Total securities in a loss position, Fair value | 3,060 | 154 |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (3) | (1) |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for less than 12 months | security | 5 |  |
Privately issued CMOs |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Available-for-sale, Less than 12 continuous months, Fair value | $ 1,310 |  |
Available-for-sale, Less than 12 continuous months, Unrealized loss | (2) |  |
Available-for-sale, Greater than 12 continuous months, Fair value | 0 |  |
Available-for-sale, Greater than 12 continuous months, Unrealized loss | 0 |  |
Available-for-sale, Total securities in a loss position, Fair value | 1,310 |  |
Available-for-sale, Total securities in a loss position, Unrealized loss | $ (2) |  |
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract] |  |  |
Number of securities in continuous loss position for less than 12 months | security | 2 |  |
MBS pass-through securities |  |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Held-to-maturity, Less than 12 continuous months, Fair value | $ 16,337 | 2,250 |
Held-to-maturity, Less than 12 continuous months, Unrealized loss | (143) | (154) |
Held-to-maturity, Greater than 12 continuous months, Fair value | 46,845 | 0 |
Held-to-maturity, Greater than 12 continuous months, Unrealized loss | (371) | 0 |
Held-to-maturity, Total securities in a loss position, Fair value | 63,182 | 2,250 |
Held-to-maturity, Total securities in a loss position, Unrealized loss | (514) | (154) |
Obligations of state and political subdivisions |  |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Held-to-maturity, Less than 12 continuous months, Fair value | 3,648 | 3,362 |
Held-to-maturity, Less than 12 continuous months, Unrealized loss | (31) | (6) |
Held-to-maturity, Greater than 12 continuous months, Fair value | 0 | 0 |
Held-to-maturity, Greater than 12 continuous months, Unrealized loss | 0 | 0 |
Held-to-maturity, Total securities in a loss position, Fair value | 3,648 | 3,362 |
Held-to-maturity, Total securities in a loss position, Unrealized loss | (31) | (6) |
CMOs issued by FHLMC |  |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Held-to-maturity, Less than 12 continuous months, Fair value | 11,066 |  |
Held-to-maturity, Less than 12 continuous months, Unrealized loss | (31) |  |
Held-to-maturity, Greater than 12 continuous months, Fair value | 13,824 |  |
Held-to-maturity, Greater than 12 continuous months, Unrealized loss | (43) |  |
Held-to-maturity, Total securities in a loss position, Fair value | 24,890 |  |
Held-to-maturity, Total securities in a loss position, Unrealized loss | (74) | 0 |
Corporate bonds |  |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |  |  |
Held-to-maturity, Less than 12 continuous months, Fair value |  | 3,518 |
Held-to-maturity, Less than 12 continuous months, Unrealized loss |  | (1) |
Held-to-maturity, Greater than 12 continuous months, Fair value |  | 0 |
Held-to-maturity, Greater than 12 continuous months, Unrealized loss |  | 0 |
Held-to-maturity, Total securities in a loss position, Fair value |  | 3,518 |
Held-to-maturity, Total securities in a loss position, Unrealized loss | $ 0 | $ (1) |

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -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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