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Investment Securities - Unrealized Loss Positions (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | $ 41,567 | $ 31,051
Greater than or equal to 12 continuous months | 105,492 | 60,669
Total Securities in a loss position | 147,059 | 91,720
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (1,285) | (205)
Greater than or equal to 12 continuous months | (4,991) | (414)
Held-to-maturity, Gross Unrealized Losses | (6,276) | (619)
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 270,513 | 212,675
Available-for-sale, greater than 12 continuous months, Fair value | 78,041 | 40,478
Available-for-sale, Total Securities in a loss position, Fair Value | 348,554 | 253,153
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (7,848) | (1,465)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (3,401) | (927)
Available-for-sale, Total Securities in a loss position, Unrealized loss | (11,249) | (2,392)
Marketable Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Marketable securities, less than 12 continuous months, Fair value | 312,080 | 243,726
Marketable securities, greater than 12 continuous months, Fair value | 183,533 | 101,147
Marketable securities, Total Securities in a loss position, Fair value | 495,613 | 344,873
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Marketable securities, less than 12 continuous months, Unrealized loss | (9,133) | (1,670)
Marketable securities, greater than 12 continuous months, Unrealized loss | (8,392) | (1,341)
Marketable securities, Total Securities in a loss position, Unrealized loss | (17,525) | (3,011)
MBS pass-through securities issued by FHLMC and FNMA |  |
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 6,602 | 16,337
Greater than or equal to 12 continuous months | 80,360 | 46,845
Total Securities in a loss position | 86,962 | 63,182
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (225) | (143)
Greater than or equal to 12 continuous months | (4,050) | (371)
Held-to-maturity, Gross Unrealized Losses | (4,275) | (514)
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 52,821 | 32,189
Available-for-sale, greater than 12 continuous months, Fair value | 20,406 | 15,325
Available-for-sale, Total Securities in a loss position, Fair Value | 73,227 | 47,514
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (1,804) | (121)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (828) | (302)
Available-for-sale, Total Securities in a loss position, Unrealized loss | (2,632) | (423)
SBA-backed securities |  |
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 8,489 |
Greater than or equal to 12 continuous months | 0 |
Total Securities in a loss position | 8,489 |
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (234) |
Greater than or equal to 12 continuous months | 0 |
Held-to-maturity, Gross Unrealized Losses | (234) |
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 23,162 | 11,028
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 165
Available-for-sale, Total Securities in a loss position, Fair Value | 23,162 | 11,193
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (893) | (53)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | (2)
Available-for-sale, Total Securities in a loss position, Unrealized loss | (893) | (55)
CMOs issued by FNMA |  |
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 11,254 |
Greater than or equal to 12 continuous months | 0 |
Total Securities in a loss position | 11,254 |
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (392) |
Greater than or equal to 12 continuous months | 0 |
Held-to-maturity, Gross Unrealized Losses | (392) |
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 13,230 | 26,401
Available-for-sale, greater than 12 continuous months, Fair value | 5,905 | 5,440
Available-for-sale, Total Securities in a loss position, Fair Value | 19,135 | 31,841
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (383) | (171)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (179) | (77)
Available-for-sale, Total Securities in a loss position, Unrealized loss | (562) | (248)
CMOs issued by FHLMC |  |
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 11,430 | 11,066
Greater than or equal to 12 continuous months | 21,438 | 13,824
Total Securities in a loss position | 32,868 | 24,890
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (400) | (31)
Greater than or equal to 12 continuous months | (901) | (43)
Held-to-maturity, Gross Unrealized Losses | (1,301) | (74)
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 87,017 | 69,276
Available-for-sale, greater than 12 continuous months, Fair value | 29,702 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 116,719 | 69,276
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (2,930) | (628)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (989) | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | (3,919) | (628)
CMOs issued by GNMA |  |
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 0 |
Greater than or equal to 12 continuous months | 3,694 |
Total Securities in a loss position | 3,694 |
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | 0 |
Greater than or equal to 12 continuous months | (40) |
Held-to-maturity, Gross Unrealized Losses | (40) |
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 10,728 | 14,230
Available-for-sale, greater than 12 continuous months, Fair value | 485 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 11,213 | 14,230
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (485) | (194)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (3) | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | (488) | (194)
Debentures of government- sponsored agencies |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 37,831 | 2,984
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 37,831 | 2,984
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (556) | (5)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | (556) | (5)
Privately issued CMOs |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value |  | 1,310
Available-for-sale, greater than 12 continuous months, Fair value |  | 0
Available-for-sale, Total Securities in a loss position, Fair Value |  | 1,310
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss |  | (2)
Available-for-sale, greater than 12 continuous months, Unrealized loss |  | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss |  | (2)
Obligations of state and political subdivisions |  |
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 3,792 | 3,648
Greater than or equal to 12 continuous months | 0 | 0
Total Securities in a loss position | 3,792 | 3,648
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (34) | (31)
Greater than or equal to 12 continuous months | 0 | 0
Held-to-maturity, Gross Unrealized Losses | (34) | (31)
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 44,714 | 52,197
Available-for-sale, greater than 12 continuous months, Fair value | 21,543 | 19,548
Available-for-sale, Total Securities in a loss position, Fair Value | 66,257 | 71,745
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (785) | (288)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (1,402) | (546)
Available-for-sale, Total Securities in a loss position, Unrealized loss | (2,187) | (834)
Corporate bonds |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 1,010 | 3,060
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 1,010 | 3,060
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (12) | (3)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (12) | $ (3)

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