Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issuable increased during the period			2,543,513
Number of shares available for future grant	4,810,271	5,570,694	5,570,694	4,810,271
Closing stock price		$ 12.43	$ 12.43
Aggregate intrinsic value of options exercised		$ 3.2	$ 7.1
Total unrecognized compensation expense of unvested options		32.6	$ 32.6
Weighted-average period of unrecognized compensation expense, unvested options			2 years 4 months 24 days
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average period of unrecognized compensation expense, unvested options			4 years
Unrecognized stock-based compensation expense related to RSUs		$ 9.0	$ 9.0
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price to fair market value common stock on grant date.			100.00%
Stock option expiration period			10 years
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance	6,134,292			6,134,292
Percentage of shares issued on common stock outstanding				4.00%
Common Stock Issuance Description			shares issuable under the 2015 Plan to the lower of (i) 4% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or (ii) a lower number determined by the board of directors.
Shares issuable increased during the period	2,543,513
Number of shares available for future grant		5,570,694	5,570,694
2015 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance	720,000			720,000
Percentage of shares issued on common stock outstanding			1.00%
Common Stock Issuance Description			shares issuable under the 2015 ESPP to the lower of (i) 1% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or (ii) a lower number determined by the board of directors.
Shares issuable increased during the period			635,878
Number of shares available for future grant		1,259,761	1,259,761
Shares purchased by employees			56,544
Shares purchased by employees, value			$ 0.5
More Than 10% Voting Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option expiration period			5 years
More Than 10% Voting Shares | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price to fair market value common stock on grant date.			110.00%