| Share-based Compensation, Stock Options, Activity [Table Text Block] |
| | | Shares | | Weighted Average Exercise Price | | Weighted Average Remaining Contractual Term (years) | | Aggregate Intrinsic Value | | | | | | | | | | (In Thousands) | | Year Ended December 31, 2017: | | | | | | | | | | | | | | | | | | Outstanding at beginning of year | | | 2,026,334 | | | $ | 9.00 | | | | 6.2 | | | $ | 57,636 | | | Granted | | | 58,000 | | | | 37.59 | | | | 9.1 | | | | 227 | | | Exercised | | | (385,500 | ) | | | 4.96 | | | | 4.0 | | | | 14,087 | | | Forfeited | | | (32,000 | ) | | | 21.96 | | | | 8.1 | | | | 625 | | | Outstanding at end of year | | | 1,666,834 | | | $ | 10.68 | | | | 5.5 | | | $ | 51,377 | | | | | | | | | | | | | | | | | | | | | Exercisable at December 31, 2017 | | | 808,236 | | | $ | 5.22 | | | | 3.9 | | | $ | 29,321 | | | | | | | | | | | | | | | | | | | | | Year Ended December 31, 2016: | | | | | | | | | | | | | | | | | | Outstanding at beginning of year | | | 2,498,834 | | | $ | 6.66 | | | | 6.3 | | | $ | 42,746 | | | Granted | | | 241,000 | | | | 20.15 | | | | 9.1 | | | | 4,166 | | | Exercised | | | (682,500 | ) | | | 4.28 | | | | 3.9 | | | | 22,629 | | | Forfeited | | | (31,000 | ) | | | 11.04 | | | | 6.8 | | | | 818 | | | Outstanding at end of year | | | 2,026,334 | | | $ | 9.00 | | | | 6.2 | | | $ | 57,636 | | | | | | | | | | | | | | | | | | | | | Exercisable at December 31, 2016 | | | 928,536 | | | $ | 5.08 | | | | 4.8 | | | $ | 30,051 | | | | | | | | | | | | | | | | | | | | | Year Ended December 31, 2015: | | | | | | | | | | | | | | | | | | Outstanding at beginning of year | | | 3,245,834 | | | $ | 4.69 | | | | 5.9 | | | $ | 38,256 | | | Granted | | | 324,000 | | | | 16.63 | | | | 9.2 | | | | 2,311 | | | Exercised | | | (1,051,000 | ) | | | 3.62 | | | | 2.7 | | | | 21,177 | | | Forfeited | | | (20,000 | ) | | | 8.40 | | | | 7.1 | | | | - | | | Outstanding at end of year | | | 2,498,834 | | | $ | 6.66 | | | | 6.3 | | | $ | 42,746 | | | | | | | | | | | | | | | | | | | | | Exercisable at December 31, 2015 | | | 410,836 | | | $ | 4.84 | | | | 5.4 | | | $ | 7,775 | | |
| Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] |
Range of
Exercise Price | | Shares | | Weighted
Average
Exercise Price | | Weighted
Average
Remaining
Contractual
Term (years) | | Aggregate
Intrinsic Value | | | | | | | | | | | | | | | | | | | (In Thousands) | | | $ | 4.17 | | | | 145,336 | | | $ | 4.17 | | | | 2.4 | | | $ | 5,426 | | | | 5.00 | | | | 483,500 | | | | 5.00 | | | | 3.8 | | | | 17,648 | | | | 5.50 | | | | 120,000 | | | | 5.50 | | | | 5.2 | | | | 4,320 | | | | 6.92 | | | | 45,000 | | | | 6.92 | | | | 6.0 | | | | 1,556 | | | | 15.74 | | | | 14,400 | | | | 15.74 | | | | 7.1 | | | | 371 | | | | | | | | 808,236 | | | | 5.22 | | | | 3.9 | | | $ | 29,321 | | |