Stock-Based Compensation - Options Activity (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Shares (in thousands)
December 31, 2017 (in shares) | shares	3,392
Granted (in shares) | shares	657
Exercised (in shares) | shares	(193)
Canceled (in shares) | shares	(19)
March 31, 2018 (in shares) | shares	3,837
Weighted- Average Exercise Price per Share
Outstanding weighted average exercise price, beginning balance (in usd per share) | $ / shares	$ 14.41
Granted weighted average exercise price (in usd per share | $ / shares	42.14
Exercised weighted average exercise price (in usd per share | $ / shares	17.78
Canceled weighted average exercise price (in usd per share | $ / shares	21.90
Outstanding weighted average exercise price, ending balance (in usd per share | $ / shares	$ 18.95