Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Restricted Stock Activity (Details)

v3.8.0.1
Stockholders' Equity - Restricted Stock Activity (Details) - Restricted Stock
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Shares [Rollforward]  
Outstanding at Beginning of Period (shares) | shares 308,700
Granted (shares) | shares 73,799
Vested (shares) | shares (187,864)
Forfeited (shares) | shares (61,341)
Outstanding at End of Period (shares) | shares 133,294
Weighted-Average Grant Date Fair Value [Roll Forward]  
Outstanding at Beginning of Period (in usd per share) | $ / shares $ 86.61
Granted (in usd per share) | $ / shares 99.53
Vested (in usd per share) | $ / shares 84.50
Forfeited (in usd per share) | $ / shares 97.78
Outstanding at End of Period (in usd per share) | $ / shares $ 91.60