Stock-Based Compensation - Summary of Stock Options (Details) - Options to purchase common stock $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Shares
Options outstanding at beginning of period (in shares) | shares	5,648
Granted (in shares) | shares	1,388
Exercised (in shares) | shares	(461)
Canceled (in shares) | shares	(407)
Expired (in shares) | shares	(409)
Options outstanding at end of period (in shares) | shares	5,759
Options exercisable at end of period (in shares) | shares	3,121
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	34.43
Exercised (in dollars per share) | $ / shares	16.14
Canceled (in dollars per share) | $ / shares	42.53
Expired (in dollars per share) | $ / shares	52.04
Options outstanding at the end of the period (in dollars per share) | $ / shares	37.29
Options exercisable at the end of the period (in dollars per share) | $ / shares	$ 36.56
Weighted- Average Contractual Life (in years)
Options outstanding at the end of period	7 years 175 days
Options exercisable at the end of period	6 years 139 days
Aggregate Intrinsic Value
Options outstanding at the end of the period (in dollars) | $	$ 5,728
Options exercisable at the end of the period (in dollars) | $	$ 5,728