Organization and Description of Business (Details) - USD ($)		9 Months Ended
	Jul. 05, 2017	Sep. 30, 2017	Dec. 31, 2016
Subsidiary, Sale of Stock [Line Items]
Net proceeds		$ 283,500,000
Offering costs		$ 5,253,000
Preferred stock outstanding	0
Gross debt related to convertible notes	$ 64,600,000
Convertible notes outstanding	$ 0
IPO
Subsidiary, Sale of Stock [Line Items]
Shares issued and sold	30,000,000
Public offering price	$ 10.00
Net proceeds	$ 278,000,000
Underwriting discounts and commissions	16,500,000
Offering costs	$ 5,500,000
Class B
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock upon conversion of Series A, B, C, and D convertible preferred stock (in shares)	85,190,551
Conversion of convertible notes into common stock	7,023,201
Authorized common stock		175,000,000	175,000,000
Common stock par value		$ 0.0001	$ 0.0001