Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Summary of Restricted Stock Activity (Details)

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Stockholders' Equity - Summary of Restricted Stock Activity (Details)
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Time based restricted stock units  
Class Of Stock [Line Items]  
Granted 42,028
Unvested restricted stock units/ awards outstanding, Ending balance 42,028
Performance and time based restricted stock units  
Class Of Stock [Line Items]  
Granted 13,109
Unvested restricted stock units/ awards outstanding, Ending balance 13,109
Restricted stock units  
Class Of Stock [Line Items]  
Granted 55,137
Unvested restricted stock units/ awards outstanding, Ending balance 55,137
Weighted-average grant date fair value per share, Granted | $ / shares $ 90.05
Weighted-average grant date fair value per share, Unvested restricted stock units/ awards outstanding, Ending balance | $ / shares $ 90.05
Time based restricted stock awards  
Class Of Stock [Line Items]  
Granted 20,789
Unvested restricted stock units/ awards outstanding, Ending balance 20,789
Unvested and expected to vest restricted stock awards outstanding 17,024
Performance and time based restricted stock awards  
Class Of Stock [Line Items]  
Granted 20,785
Unvested restricted stock units/ awards outstanding, Ending balance 20,785
Unvested and expected to vest restricted stock awards outstanding 17,027
Restricted stock awards  
Class Of Stock [Line Items]  
Granted 41,574
Unvested restricted stock units/ awards outstanding, Ending balance 41,574
Unvested and expected to vest restricted stock awards outstanding 34,051
Weighted-average grant date fair value per share, Granted | $ / shares $ 91.52
Weighted-average grant date fair value per share, Unvested restricted stock units/ awards outstanding, Ending balance | $ / shares 91.52
Weighted-average grant date fair value per share, Unvested and expected to vest restricted stock awards outstanding | $ / shares $ 91.52