Common Stock and Stockholders' Equity (Deficit) - Capitalization (Details) $ / shares in Units, $ in Millions	Jul. 07, 2015 USD ($) $ / shares shares	Jun. 17, 2015 USD ($) $ / shares shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2015 $ / shares shares
Capitalization
Common stock par value (in dollars per share) | $ / shares			$ 0.001	$ 0.001
Reverse stock split		0.437
Number of common stock shares authorized		75,000,000	75,000,000	75,000,000
Number of preferred stock shares authorized		50,479,286
Number of shares issued upon conversion of convertible stock	25,500,000
Convertible Preferred Stock
Capitalization
Share price threshold of initial public offering for automatic conversion into common stock (in dollars per share) | $ / shares		$ 12.00
Threshold of proceeds from initial public offering for automatic conversion into common stock | $		$ 75.0
Number of shares issued upon conversion of convertible stock	25,500,000
IPO And Over-Allotment Option
Capitalization
Issuance of stock (in shares)	9,487,500	9,487,500
Price of stock issued (in dollars per share) | $ / shares	$ 19.00	$ 19.00
Proceeds received, net of issuance costs | $	$ 163.1	$ 163.1
Underwriting discounts and commissions | $	12.6	12.6
Other offering expenses | $	$ 4.5	$ 4.5