| Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] |
| | | Three Months Ended September 30, | | Nine Months Ended September 30, | | | | 2018 | | 2017 | | 2018 | | 2017 | | | | (In Thousands, Except Shares and Per Share Data) | | Earnings per common share | | | | | | | | | | | | | | | | | | Weighted average common shares outstanding | | | 53,171,144 | | | | 52,950,644 | | | | 53,134,861 | | | | 52,854,332 | | | Net income available to common stockholders | | $ | 34,560 | | | $ | 25,259 | | | $ | 100,672 | | | $ | 71,911 | | | Basic earnings per common share | | $ | 0.65 | | | $ | 0.48 | | | $ | 1.89 | | | $ | 1.36 | | | | | | | | | | | | | | | | | | | | | Weighted average common shares outstanding | | | 53,171,144 | | | | 52,950,644 | | | | 53,134,861 | | | | 52,854,332 | | | Dilutive effects of assumed conversions and exercise of stock options and warrants | | | 1,020,078 | | | | 1,149,028 | | | | 1,055,383 | | | | 1,256,580 | | | Weighted average common and dilutive potential common shares outstanding | | | 54,191,222 | | | | 54,099,672 | | | | 54,190,244 | | | | 54,110,912 | | | Net income available to common stockholders | | $ | 34,560 | | | $ | 25,259 | | | $ | 100,672 | | | $ | 71,911 | | | Diluted earnings per common share | | $ | 0.64 | | | $ | 0.47 | | | $ | 1.86 | | | $ | 1.33 | | |