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Investment (Held-to-Maturity) Securities (Details) $ in Thousands | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2018 USD ($) | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($)
Schedule of Investment (Held-to-Maturity) Securities [Line Items] |  |  |  |
Investments Securities, Amortized Cost |  | $ 374,039 | $ 461,793 | $ 466,562
Investment Securities, fair value |  | 382,893 | 480,035 | 489,895
Investment Securities, Gross Unrealized Gain |  | 12,329 | 20,508 | 24,150
Investment Securities, Gross Unrealized Loss |  | (3,475) | (2,266) | (817)
Investment Securities, Debt Maturities, Net Carrying Value [Abstract] |  |  |  |
Investments Securities, Debt Maturities, Amortized Cost |  | 374,039 | 461,793 | 466,562
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Fair Value |  | $ 382,893 | $ 480,035 | $ 489,895
Investment Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Nominal Yield |  | 4.36% |  |
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 181 | 150 | 92
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 91,741 | $ 166,051 | $ 93,835
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 61,488 | 12,265 | 10,222
Investment Securities, Continuous Unrealized Loss Position, Fair Value |  | 153,229 | 178,316 | 104,057
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 2,408 | 1,881 | 698
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 1,067 | 385 | 119
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 3,475 | 2,266 | 817
Fixed Maturity Securities [Member] |  |  |  |
Investment Securities, Debt Maturities, Net Carrying Value [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value |  | 80,636 |  |
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value |  | 102,652 |  |
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value |  | 151,239 |  |
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value |  | 26,278 |  |
Investment Securities, Debt Maturities, Single Maturity Date, Net Carrying Value |  | 360,805 |  |
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less Than One Year, Fair Value |  | 80,574 |  |
Investment Securities, Debt Maturities, One to Five Years, Fair Value |  | 104,036 |  |
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 159,913 |  |
Investment Securities, Debt Maturities, Over Ten Years, Fair Value |  | 25,169 |  |
Investment Securities, Debt Maturities, Single Maturity Date, Fair Value |  | $ 369,692 |  |
Investment Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield |  | 2.44% |  |
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield |  | 3.94% |  |
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield |  | 5.82% |  |
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield |  | 4.33% |  |
Investment Securities, Debt Maturities, Nominal Yield |  | 4.42% |  |
Investment Securities, Debt Maturities, Weighted Average Maturity | [1] | 5.88 |  |
Municipal and other tax-exempt securities [Member] |  |  |  |
Schedule of Investment (Held-to-Maturity) Securities [Line Items] |  |  |  |
Investments Securities, Amortized Cost |  | $ 157,723 | 228,186 | 246,000
Investment Securities, fair value |  | 158,230 | 230,349 | 249,250
Investment Securities, Gross Unrealized Gain |  | 1,403 | 2,967 | 3,415
Investment Securities, Gross Unrealized Loss |  | (896) | (804) | (165)
Investment Securities, Debt Maturities, Net Carrying Value [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value |  | 65,789 |  |
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value |  | 41,827 |  |
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value |  | 35,652 |  |
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value |  | 14,455 |  |
Investment Securities, Debt Maturities, Single Maturity Date, Net Carrying Value |  | 157,723 |  |
Investments Securities, Debt Maturities, Amortized Cost |  | 157,723 | 228,186 | 246,000
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less Than One Year, Fair Value |  | 65,633 |  |
Investment Securities, Debt Maturities, One to Five Years, Fair Value |  | 41,432 |  |
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 36,677 |  |
Investment Securities, Debt Maturities, Over Ten Years, Fair Value |  | 14,488 |  |
Investment Securities, Debt Maturities, Single Maturity Date, Fair Value |  | 158,230 |  |
Investment Securities, Debt Maturities, Fair Value |  | $ 158,230 | $ 230,349 | $ 249,250
Investment Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield | [2] | 2.06% |  |
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield | [2] | 2.82% |  |
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield | [2] | 6.00% |  |
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield | [2] | 4.33% |  |
Investment Securities, Debt Maturities, Nominal Yield | [2] | 3.36% |  |
Investment Securities, Debt Maturities, Weighted Average Maturity | [1] | 4.13 |  |
Investment Securities,Debt Maturities, Effective tax rate for nominal yield calculation |  | 25.00% |  |
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 85 | 100 | 63
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 46,618 | $ 145,960 | $ 80,235
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 54,149 | 5,833 | 9,795
Investment Securities, Continuous Unrealized Loss Position, Fair Value |  | 100,767 | 151,793 | 90,030
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 277 | 643 | 70
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 619 | 161 | 95
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 896 | 804 | 165
Other debt securities [Member] |  |  |  |
Schedule of Investment (Held-to-Maturity) Securities [Line Items] |  |  |  |
Investments Securities, Amortized Cost |  | 203,082 | 217,716 | 203,636
Investment Securities, fair value |  | 211,462 | 233,444 | 223,187
Investment Securities, Gross Unrealized Gain |  | 10,721 | 17,095 | 20,141
Investment Securities, Gross Unrealized Loss |  | (2,341) | (1,367) | (590)
Investment Securities, Debt Maturities, Net Carrying Value [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value |  | 14,847 |  |
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value |  | 60,825 |  |
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value |  | 115,587 |  |
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value |  | 11,823 |  |
Investment Securities, Debt Maturities, Single Maturity Date, Net Carrying Value |  | 203,082 |  |
Investments Securities, Debt Maturities, Amortized Cost |  | 203,082 | 217,716 | 203,636
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less Than One Year, Fair Value |  | 14,941 |  |
Investment Securities, Debt Maturities, One to Five Years, Fair Value |  | 62,604 |  |
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 123,236 |  |
Investment Securities, Debt Maturities, Over Ten Years, Fair Value |  | 10,681 |  |
Investment Securities, Debt Maturities, Single Maturity Date, Fair Value |  | 211,462 |  |
Investment Securities, Debt Maturities, Fair Value |  | $ 211,462 | $ 233,444 | $ 223,187
Investment Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield |  | 4.17% |  |
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield |  | 4.70% |  |
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield |  | 5.76% |  |
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield |  | 4.34% |  |
Investment Securities, Debt Maturities, Nominal Yield |  | 5.25% |  |
Investment Securities, Debt Maturities, Weighted Average Maturity | [1] | 7.23 |  |
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 93 | 49 | 28
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 38,441 | $ 20,091 | $ 10,022
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 4,714 | 3,076 | 427
Investment Securities, Continuous Unrealized Loss Position, Fair Value |  | 43,155 | 23,167 | 10,449
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 2,035 | 1,238 | 566
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 306 | 129 | 24
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 2,341 | 1,367 | 590
U.S. government agency residential mortgage-backed securities [Member] |  |  |  |
Schedule of Investment (Held-to-Maturity) Securities [Line Items] |  |  |  |
Investments Securities, Amortized Cost |  | 13,234 | 15,891 | 16,926
Investment Securities, fair value |  | 13,201 | 16,242 | 17,458
Investment Securities, Gross Unrealized Gain |  | 205 | 446 | 594
Investment Securities, Gross Unrealized Loss |  | (238) | (95) | (62)
Investment Securities, Debt Maturities, Net Carrying Value [Abstract] |  |  |  |
Investment Securities, Debt Maturities, without Single Maturity Date, Net Carrying Value |  | 13,234 |  |
Investments Securities, Debt Maturities, Amortized Cost |  | 13,234 | 15,891 | 16,926
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |
Investment Securities, Debt Maturities, without Single Maturity Date, Fair Value |  | 13,201 |  |
Investment Securities, Debt Maturities, Fair Value |  | $ 13,201 | $ 16,242 | $ 17,458
Investment Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |
Investment Securities, Debt Maturities, Nominal Yield | [3] | 2.77% |  |
Investment Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities |  | 5 years 2 months 12 days |  |
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 3 | 1 | 1
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 6,682 | $ 0 | $ 3,578
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 2,625 | 3,356 | 0
Investment Securities, Continuous Unrealized Loss Position, Fair Value |  | 9,307 | 3,356 | 3,578
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 96 | 0 | 62
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 142 | 95 | 0
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | $ 238 | $ 95 | $ 62
[1] | Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.
[2] | Calculated on a taxable equivalent basis using a 25 percent effective tax rate.
[3] | The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio.

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- Definition Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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- Definition Amount of investment in debt security measured at amortized cost (held-to-maturity), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date. + References No definition available. + Details
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