Stock-Based Compensation (Details)		1 Months Ended	5 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2015 shares	Jun. 30, 2015 shares	Apr. 30, 2016 USD ($) shares	Oct. 31, 2016 USD ($) shares	Dec. 31, 2017 USD ($) $ / shares period shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Jun. 30, 2017 shares
Stock Based Compensation
Stock option shares approved								425,000
2015 Plan
Stock Based Compensation
Shares reserved for issuance		3,451,495			14,567,816
Shares reserved for issuance as a proportion common stock outstanding (as a percent)					4.00%
2015 Plan | Minimum
Stock Based Compensation
Shares reserved for issuance					3,500,000
2007 Plan
Stock Based Compensation
Stock options, exercise price range, number outstanding (in shares)					5,551,616
Stock options, exercise price range, lower range limit (in dollars per share) | $ / shares					$ 0.0978
Stock options, exercise price range, upper range limit (in dollars per share) | $ / shares					$ 12.8501
Employee stock purchase plan
Stock Based Compensation
Shares reserved for issuance		893,548			1,136,615
Shares reserved for issuance as a proportion common stock outstanding (as a percent)					1.00%
Price in relation to fair market value of common stock on the date of grant, lower range limit (as a percent)					85.00%
Maximum number of shares a participant may receive during the period (in shares)					5,000
Maximum amount of award or purchase during a calendar year | $					$ 25,000
Maximum offering period, term					27 months
Number of expected offering periods each year | period					2
Offering period, expected term					6 months
Issuance of common stock under employee stock purchase plan (in shares)			211,729	234,452
Proceeds from issuance of common stock under employee stock purchase plan | $			$ 1,500,000	$ 1,800,000
Maximum employee contribution of employee's cash compensation (as a percent)					15.00%
Employee stock purchase plan | Minimum
Stock Based Compensation
Shares reserved for issuance					880,000
Performance-baseed awards
Stock Based Compensation
Stock option shares approved								200,000
Employee and non-employee stock options
Stock Based Compensation
Stock-based compensation expense | $					$ 11,402,000	$ 10,601,000	$ 7,326,000
Shares available for issuance					4,737,000	4,115,000
Employee and non-employee stock options | 2015 Plan
Stock Based Compensation
Vesting period					4 years
Expiration period		10 years
Employee and non-employee stock options | 2007 Plan
Stock Based Compensation
Shares exercised and unvested	1,300,000
Period after Market Stand-off repurchase right expires							210 days
Accelerated stock-based compensation expense | $							$ 1,300,000
Stock appreciation rights | 2015 Plan
Stock Based Compensation
Vesting period					4 years
Expiration period					10 years
Restricted stock units
Stock Based Compensation
Shares granted					345