Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2018	May 08, 2018	Dec. 31, 2017
Liabilities:
Warrant liability			$ 2,766
Series D preferred stock warrants
Liabilities:
Warrants, type			us-gaap:RedeemablePreferredStockMember
Common stock warrants
Liabilities:
Warrants, type		us-gaap:CommonStockMember	us-gaap:CommonStockMember
Recurring basis
Assets:
Cash equivalents	$ 166,173		$ 21,597
Fair value of assets	166,173
Recurring basis | Series D preferred stock warrants
Liabilities:
Warrant liability			1,774
Recurring basis | Common stock warrants
Liabilities:
Warrant liability			2,766
Level 1 | Recurring basis
Assets:
Cash equivalents	166,173		21,597
Fair value of assets	$ 166,173
Level 3 | Recurring basis | Series D preferred stock warrants
Liabilities:
Warrant liability			1,774
Level 3 | Recurring basis | Common stock warrants
Liabilities:
Warrant liability			$ 2,766