| Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] |
| | | Three Months Ended September 30, | | Nine Months Ended September 30, | | | | 2017 | | 2016 | | 2017 | | 2016 | | | | (In Thousands, Except Shares and Per Share Data) | | Earnings per common share | | | | | | | | | | | | | | | | | | Weighted average common shares outstanding | | | 52,950,644 | | | | 52,554,918 | | | | 52,854,332 | | | | 52,557,910 | | | Net income available to common stockholders | | $ | 25,259 | | | $ | 20,909 | | | $ | 71,911 | | | $ | 59,718 | | | Basic earnings per common share | | $ | 0.48 | | | $ | 0.40 | | | $ | 1.36 | | | $ | 1.14 | | | | | | | | | | | | | | | | | | | | | Weighted average common shares outstanding | | | 52,950,644 | | | | 52,554,918 | | | | 52,854,332 | | | | 52,557,910 | | | Dilutive effects of assumed conversions and exercise of stock options and warrants | | | 1,149,028 | | | | 1,324,410 | | | | 1,256,580 | | | | 932,008 | | | Weighted average common and dilutive potential common shares outstanding | | | 54,099,672 | | | | 53,879,328 | | | | 54,110,912 | | | | 53,489,918 | | | Net income available to common stockholders | | $ | 25,259 | | | $ | 20,909 | | | $ | 71,911 | | | $ | 59,718 | | | Diluted earnings per common share | | $ | 0.47 | | | $ | 0.39 | | | $ | 1.33 | | | $ | 1.12 | | |