Stock-Based Compensation - Employee Stock Purchase Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Weighted-average remaining contractual term (in years)
Stock-based compensation expense	$ 23,508	$ 11,685	$ 41,909	$ 21,146
2012 ESPP
Weighted-average remaining contractual term (in years)
Shares reserved for issuance under ESPP	275,000		275,000
Number of shares remaining available for grant	176,561		176,561
Shares issued under ESPP			17,684	25,225
Stock-based compensation expense			$ 1,000	$ 500