Schedule of Stock Option Activity [Table Text Block] |
The following tables summarize our outstanding stock options: | | | | | | | | | | | | | | | | | Weighted Average | | | | Number |
| | Weighted Average | | Remaining | | Aggregate |
| | of Shares |
| | Exercise Price | | Contractual Life (Years) | | Intrinsic Value |
| Outstanding December 31, 2014 | 871,671 |
| | $60.43 | | | | | Options granted under 2012 Plan | 450,000 |
| | $72.11 | | | | | Options granted under 2005 Plan | 20,000 |
| | $72.11 | | | | | Options exercised under 2005 Plan | (66,670 | ) | | $46.87 | | | | | Options exercised under 2012 Plan | (421,657 | ) | | $63.03 | | | | | Options canceled under 2012 Plan | (111,668 | ) | | $71.95 | | | | | Outstanding December 31, 2015 | 741,676 |
| | $60.43 | | | | | Options granted under 2012 Plan | 470,000 |
| | $60.78 | | | | | Options exercised under 2005 Plan | (61,666 | ) | | $52.36 | | | | | Options exercised under 2012 Plan | (608,331 | ) | | $65.18 | | | | | Outstanding December 31, 2016 | 541,679 |
| | $65.84 | | | | | Options granted under 2012 Plan | 495,000 |
| | $74.90 | | | | | Options exercised under 2005 Plan | (15,000 | ) | | $47.52 | | | | | Options exercised under 2012 Plan | (155,829 | ) | | $65.73 | | | | | Options canceled under 2012 Plan | (6,668 | ) | | $60.52 | | | | | Outstanding December 31, 2017 | 859,182 |
| | $70.11 | | 3.39 | | $ | 4,531,000 |
| | | | | | | | | Exercisable December 31, 2017 | 465,831 |
| | $69.85 | | 3.01 | | $ | 2,578,000 |
|
| | | | | | | | | | | | | | | | | Remaining | Grant | | Number |
| | Exercise |
| | Contractual | Date | | of Shares |
| | Price |
| | Life in Years | 2/25/2013 | | 15,000 |
| | $ | 64.49 |
| | 0.15 | 2/25/2014 | | 48,334 |
| | $ | 61.31 |
| | 1.15 | 2/20/2015 | | 120,004 |
| | $ | 72.11 |
| | 2.14 | 2/22/2016 | | 185,842 |
| | $ | 60.52 |
| | 3.15 | 3/8/2016 | | 26,667 |
| | $ | 63.63 |
| | 3.19 | 2/22/2017 | | 453,335 |
| | $ | 74.78 |
| | 4.15 | 9/1/2017 | | 10,000 |
| | $ | 80.55 |
| | 4.68 | Outstanding December 31, 2017 | | 859,182 |
| | | | |
|
Schedule of Nonvested Share Activity [Table Text Block] |
The following table summarizes our outstanding non-vested stock options: | | | | | | | Number of Shares |
| | Weighted Average Grant Date Fair Value | Non-vested December 31, 2016 | 353,348 |
| | $3.99 | Options granted under 2012 Plan | 495,000 |
| | $5.76 | Options vested under 2012 Plan | (441,661 | ) | | $4.98 | Options vested under 2005 Plan | (6,668 | ) | | $4.91 | Non-vested options canceled under 2012 Plan | (6,668 | ) | | $3.61 | Non-vested December 31, 2017 | 393,351 |
| | $5.10 |
|