Weichai Transactions (Details) - Share Purchase Agreement, Weichai Transaction	1 Months Ended			12 Months Ended
	Nov. 30, 2017 shares	Aug. 31, 2017 shares	Mar. 31, 2017 USD ($) shares	Dec. 31, 2017 shares
Subsidiary, Sale of Stock [Line Items]
Consideration received on transaction | $			$ 60,000,000
Common Stock
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)			2,728,752	2,729,000
Common Stock | Chief Strategy Officer
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)		200,000
Redeemable Convertible Series B Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)			2,385,624
Debt instrument, convertible, conversion ratio			2
Issuance of redeemable convertible Series B Preferred Stock, net of fees (in shares)	4,771,248			4,771,000