Description of Business and Summary of Significant Accounting Policies - Narrative (Details) $ / shares in Units, $ in Thousands		6 Months Ended	12 Months Ended
	Aug. 02, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock issued upon conversion (in shares) | shares	55,422,002
Conversion basis	1
Initial public offering costs			$ 3,708
Accumulated deficit		$ 162,235	129,003
Additional Paid-in Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Initial public offering costs			$ 3,708
IPO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shares sold in offering (in shares) | shares	10,615,650
Offering price (in dollars per share) | $ / shares	$ 15.00
Net proceeds from stock offering	$ 144,380
IPO | Additional Paid-in Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Initial public offering costs		$ 3,708
Over-Allotment Option
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shares sold in offering (in shares) | shares	1,384,650