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Stockholders' Equity - Shares Repurchased (Details) - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Equity, Class of Treasury Stock [Line Items]        
Number of shares repurchased related to withholding taxes due on accelerated vesting of RSUs (in shares) 26,741   26,741  
Average share price (in usd per share) $ 31.80   $ 31.80  
Shares Related to Withholding Taxes on the Vesting of Restricted Stock        
Equity, Class of Treasury Stock [Line Items]        
Repurchased shares to pay withholding taxes (in shares) 368 344 53,188 27,711
Stock repurchase to pay withholding taxes average share price (in usd per share) $ 36.34 $ 25.80 $ 31.99 $ 24.61