Share-Based Compensation - Activity (Details) - USD ($) | Feb. 22, 2016 | Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2015 |
Restricted Stock Awards | | | | |
Restricted Stock Awards, Number of Shares | | | | |
Balance at beginning of period (in shares) | | 586,600 | | |
Granted (in shares) | | 317,200 | | |
Converted/Exercised (in shares) | | (152,100) | | |
Forfeited (in shares) | | (1,200) | | |
Balance at end of period (in shares) | | 750,500 | | |
Restricted Stock Awards, Weighted Average Grant Date Fair Value Per Share | | | | |
Balance at beginning of period (in dollars per share) | | $ 21.97 | | |
Granted (in dollars per share) | | 28.41 | | |
Converted/Exercised (in dollars per share) | | 19.16 | | |
Forfeited (in dollars per share) | | 23.20 | | |
Balance at end of period (in dollars per share) | | $ 25.25 | | |
Restricted stock awards, additional disclosures | | | | |
Unrecognized compensation expense related to unvested restricted stock awards | | $ 16,800,000 | | |
Weighted average remaining vesting period | | 2 years 2 months 12 days | | |
Assumptions used to estimate the fair values of the awards granted: | | | | |
Remaining measurement period | | 2 years 10 months 10 days | | |
Risk free interest rate (as a percent) | | 0.90% | | |
Dividend yield (as a percent) | | 0.00% | | |
Estimated fair value of awards granted (in dollars per share) | | $ 33.77 | | |
Stock Options | | | | |
Stock Options, Number of Shares | | | | |
Balance at beginning of period (in shares) | | 387,600 | | |
Granted (in shares) | | 409,300 | | |
Balance at end of period (in shares) | | 796,900 | | |
Stock Options, Weighted Average Grant Date Fair Value Per Share | | | | |
Balance at beginning of period (in dollars per share) | | $ 9.35 | | |
Granted (in dollars per share) | | 10.20 | | |
Balance at end of period (in dollars per share) | | 9.79 | | |
Stock Options, Weighted Average Exercise Price Per Share | | | | |
Balance at beginning of period (in dollars per share) | | 24.03 | | |
Granted (in dollars per share) | | 26.30 | | |
Balance at end of period (in dollars per share) | | $ 25.20 | | |
Stock options, additional disclosures | | | | |
Aggregate intrinsic value | | $ 3,620,400 | | $ 2,611,700 |
Unrecognized compensation expense related to unvested stock options | | $ 6,800,000 | | |
Weighted average remaining vesting period | | 2 years 3 months 18 days | | |
Weighted average remaining contractual life | | 9 years 4 months 24 days | | |
Exercisable, Number of shares | | 71,700 | | |
Exercisable, Weighted Average Grant Date Fair Value Per Share | | $ 6.69 | | |
Exercisable Weighted Average Exercise Price Per Share | | $ 16.86 | | |
Exercisable, Aggregate Intrinsic Value | | $ 923,900 | | |
Assumptions used to estimate the fair values of the awards granted: | | | | |
Risk free interest rate (as a percent) | | 1.51% | 1.82% | |
Expected volatility (as a percent) | | 38.00% | 37.00% | |
Expected life (in years) | | 6 years | 6 years | |
Dividend yield (as a percent) | | 0.00% | 0.00% | |
Estimated fair value of awards granted (in dollars per share) | | $ 10.20 | $ 10.44 | |
Performance-based conditions | Restricted Stock Awards | | | | |
Restricted stock awards, additional disclosures | | | | |
Grant date fair value | $ 2,351,700 | | | |
Performance-based conditions | Restricted Stock Awards | Payout Range-0% | | | | |
Restricted stock awards, additional disclosures | | | | |
Payout range (as a percent) | 0.00% | | | |
Performance-based conditions | Restricted Stock Awards | Payout Range-25% | | | | |
Restricted stock awards, additional disclosures | | | | |
Payout range (as a percent) | 25.00% | | | |
Related expenses | $ 587,900 | | | |
Performance-based conditions | Restricted Stock Awards | Payout Range-100% | | | | |
Restricted stock awards, additional disclosures | | | | |
Payout range (as a percent) | 100.00% | | | |
Related expenses | $ 2,351,700 | | | |
Performance-based conditions | Restricted Stock Awards | Payout Range-200% | | | | |
Restricted stock awards, additional disclosures | | | | |
Payout range (as a percent) | 200.00% | | | |
Related expenses | $ 4,703,400 | | | |