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Stock-Based Awards and Other Equity Instruments - Summary of Restricted Stock Units Activity (Details) - RSUs - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
RSUs      
Beginning balance (in shares) 1,349 1,396 337
Granted (in shares) 1,350 691 1,643
Vested (in shares) (492) (516) (493)
Cancelled (in shares) (266) (222) (91)
Ending balance (in shares) 1,941 1,349 1,396
Weighted Average Grant-Date Fair Value      
Beginning balance (in dollars per share) $ 114.58 $ 119.20 $ 61.97
Granted (in dollars per share) 123.24 109.38 123.42
Vested (in dollars per share) 115.29 118.71 103.73
Cancelled (in dollars per share) 116.26 117.84 67.11
Ending balance (in dollars per share) $ 120.19 $ 114.58 $ 119.20