Stock-Based Compensation - Summary of Stock Options (Details) - Options to purchase common stock $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Shares
Options outstanding at beginning of period (in shares) | shares	5,648
Granted (in shares) | shares	1,098
Exercised (in shares) | shares	(445)
Canceled (in shares) | shares	(265)
Expired (in shares) | shares	(307)
Options outstanding at end of period (in shares) | shares	5,729
Options exercisable at end of period (in shares) | shares	2,965
Weighted- Average Exercise Price (in dollars per share)
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 37.71
Granted (in dollars per share) | $ / shares	37.43
Exercised (in dollars per share) | $ / shares	16.43
Canceled (in dollars per share) | $ / shares	43.90
Expired (in dollars per share) | $ / shares	51.53
Options outstanding at the end of the period (in dollars per share) | $ / shares	38.91
Options exercisable at the end of the period (in dollars per share) | $ / shares	$ 36.27
Weighted- Average Contractual Life (in years)
Options outstanding at the end of period	7 years 245 days
Options exercisable at the end of period	6 years 215 days
Aggregate Intrinsic Value
Options outstanding at the end of the period (in dollars) | $	$ 13,536
Options exercisable at the end of the period (in dollars) | $	$ 13,280