Stock-Based Compensation Plans (Details) - USD ($) |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Stock based compensation plans: | ||||
| Stock-based compensation expense | $ 2,048,817 | $ 4,706,489 | $ 11,158,738 | $ 9,211,324 |
| Tax benefits from stock-based compensation expense | $ 776,092 | $ 1,763,992 | $ 4,226,930 | $ 3,437,654 |
| Grants in period, options (in shares) | 0 | 0 | ||
| Restricted stock | ||||
| Stock based compensation plans: | ||||
| Grants in period, other than options (in shares) | 251,221 | 677,091 | ||
| Performance and market-based stock | ||||
| Stock based compensation plans: | ||||
| Grants in period, other than options (in shares) | 91,612 | 69,213 | ||