Stock Options, Restricted Stock Units and Employee Stock Purchase Plan - Non-vested Restricted Stock Activity (Details) - Restricted stock units shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Number of Units
Non-vested shares, beginning balance (in Shares) | shares	888
Granted (in Shares) | shares	1,308
Vested (in Shares) | shares	(170)
Forfeited (in Shares) | shares	(63)
Non-vested shares, ending balance (in Shares) | shares	1,963
Weighted Average Per Share Grant Date Fair Value
Weighted average grant date fair value, beginning balance (in Dollars per share) | $ / shares	$ 32.56
Granted (in Dollars per share) | $ / shares	19.28
Vested (in Dollars per share) | $ / shares	32.40
Forfeited (in Dollars per share) | $ / shares	25.09
Weighted average grant date fair value, ending balance (in Dollars per share) | $ / shares	$ 23.96