Stock-Based Compensation - Stock Options (Details) - Outstanding stock awards and Employee Stock Purchase Plan $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Shares
Outstanding at the beginning of the period (in shares) | shares	6,978,621
Granted (in shares) | shares	491,590
Exercised (in shares) | shares	(78,251)
Cancelled (in shares) | shares	(44,280)
Outstanding at the end of the period (in shares) | shares	7,347,680
Vested at the end of the period (in shares) | shares	3,634,361
Weighted-average price per share
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 40.65
Granted (in dollars per share) | $ / shares	167.45
Exercised (in dollars per share) | $ / shares	42.59
Cancelled (in dollars per share) | $ / shares	45.22
Outstanding at the end of the period (in dollars per share) | $ / shares	49.09
Vested at the end of the period (in dollars per share) | $ / shares	$ 26.90
Total unrecognized compensation cost related to unvested stock options (in dollars) | $	$ 143.4
Weighted average period over which unrecognized compensation costs are expected to be recognized	2 years 7 months 6 days