| Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] |
| | | Fair Value Measurements at December 31, 2018 Using | | | | Quoted Prices in | | | | | | | | | | Active Markets | | Significant Other | | Significant | | | | | | for Identical | | Observable Inputs | | Unobservable | | | | | | Assets (Level 1) | | (Level 2) | | Inputs (Level 3) | | Total | | Assets Measured on a Recurring Basis: | | | | Available-for-sale securities: | | | | | | | | | | | | | | | | | | U.S. Treasury and government sponsored agencies | | $ | - | | | $ | 76,993 | | | $ | - | | | $ | 76,993 | | | Mortgage-backed securities | | | - | | | | 304,304 | | | | - | | | | 304,304 | | | State and municipal securities | | | - | | | | 105,994 | | | | - | | | | 105,994 | | | Corporate debt | | | - | | | | 96,375 | | | | 6,518 | | | | 102,893 | | | Total assets at fair value | | $ | - | | | $ | 583,666 | | | $ | 6,518 | | | $ | 590,184 | | | | | Fair Value Measurements at December 31, 2017 Using | | | | Quoted Prices in | | | | | | | | | | Active Markets | | Significant Other | | Significant | | | | | | for Identical | | Observable Inputs | | Unobservable | | | | | | Assets (Level 1) | | (Level 2) | | Inputs (Level 3) | | Total | | Assets Measured on a Recurring Basis: | | | | Available-for-sale securities | | | | | | | | | | | | | | | | | | U.S. Treasury and government sponsored agencies | | $ | - | | | $ | 55,356 | | | $ | - | | | $ | 55,356 | | | Mortgage-backed securities | | | - | | | | 276,498 | | | | - | | | | 276,498 | | | State and municipal securities | | | - | | | | 134,849 | | | | - | | | | 134,849 | | | Corporate debt | | | - | | | | 64,877 | | | | 6,500 | | | | 71,377 | | | Total assets at fair value | | $ | - | | | $ | 531,580 | | | $ | 6,500 | | | $ | 538,080 | | |
| Fair Value Measurements, Nonrecurring [Table Text Block] |
| | | Fair Value Measurements at December 31, 2018 Using | | | | Quoted Prices in | | | | | | | | | | Active Markets | | Significant Other | | Significant | | | | | | for Identical | | Observable | | Unobservable | | | | | | Assets (Level 1) | | Inputs (Level 2) | | Inputs (Level 3) | | Total | | Assets Measured on a Nonrecurring Basis: | | | | Impaired loans | | $ | - | | | | - | | | $ | 30,463 | | | $ | 30,463 | | | Other real estate owned and repossessed assets | | | - | | | | - | | | | 5,169 | | | | 5,169 | | | Total assets at fair value | | | - | | | | - | | | $ | 35,632 | | | $ | 35,632 | | | | | Fair Value Measurements at December 31, 2017 Using | | | | Quoted Prices in | | | | | | | | | | Active Markets | | Significant Other | | Significant | | | | | | for Identical | | Observable | | Unobservable | | | | | | Assets (Level 1) | | Inputs (Level 2) | | Inputs (Level 3) | | Total | | Assets Measured on a Nonrecurring Basis: | | | | Impaired loans | | $ | - | | | $ | - | | | $ | 34,901 | | | $ | 34,901 | | | Other real estate owned | | | - | | | | - | | | | 6,701 | | | | 6,701 | | | Total assets at fair value | | $ | - | | | $ | - | | | $ | 41,602 | | | $ | 41,602 | | |
| Fair Value, by Balance Sheet Grouping [Table Text Block] |
| | | December 31, | | | | 2018 | | 2017 | | | | Carrying Amount | | Fair Value | | Carrying Amount | | Fair Value | | | | (In Thousands) | | Financial Assets: | | | | | | | | | | | | | | | | | | Level 1 Inputs: | | | | | | | | | | | | | | | | | | Cash and cash equivalents | | $ | 458,050 | | | $ | 458,050 | | | $ | 238,062 | | | $ | 238,062 | | | | | | | | | | | | | | | | | | | | | Level 2 Inputs: | | | | | | | | | | | | | | | | | | Debt securities available for sale | | $ | 583,666 | | | $ | 583,666 | | | $ | 531,580 | | | $ | 531,580 | | | Equity securities | | | 894 | | | | 894 | | | | 1,034 | | | | 1,034 | | | Federal funds sold | | | 223,845 | | | | 223,845 | | | | 239,524 | | | | 239,524 | | | Mortgage loans held for sale | | | 120 | | | | 121 | | | | 4,459 | | | | 4,459 | | | Bank owned life insurance contracts | | | 130,649 | | | | 130,649 | | | | 127,519 | | | | 127,519 | | | | | | | | | | | | | | | | | | | | | Level 3 Inputs: | | | | | | | | | | | | | | | | | | Debt securities available for sale | | $ | 6,518 | | | $ | 6,518 | | | $ | 6,500 | | | $ | 6,500 | | | Debt securities held to maturity | | | - | | | | - | | | | 250 | | | | 250 | | | Loans, net | | | 6,464,899 | | | | 6,398,604 | | | | 5,791,855 | | | | 5,747,342 | | | | | | | | | | | | | | | | | | | | | Financial Liabilities: | | | | | | | | | | | | | | | | | | Level 2 Inputs: | | | | | | | | | | | | | | | | | | Deposits | | $ | 6,915,708 | | | $ | 6,910,176 | | | $ | 6,091,674 | | | $ | 6,086,085 | | | Federal funds purchased | | | 288,725 | | | | 288,725 | | | | 301,797 | | | | 301,797 | | | Other borrowings | | | 64,666 | | | | 64,613 | | | | 64,832 | | | | 65,921 | | |