Stockholders' Equity - Common and Treasury Stock and Series B Convertible Preferred Stock (Details) - shares			6 Months Ended
	May 03, 2019	Apr. 23, 2019	Jun. 30, 2019
Common Shares Issued
Common stock, issued, beginning balance (in shares)			19,067,000
Common stock, issued, ending balance (in shares)			23,117,000
Treasury Stock Shares
Treasury stock shares, beginning balance (in shares)			429,000
Treasury stock shares issued (in shares)			(137,000)
Treasury stock shares, ending balance (in shares)			292,000
Common Shares Outstanding
Common stock, outstanding, beginning balance (in shares)			18,638,000
Common stock, outstanding, ending balance (in shares)			22,825,000
Common Stock
Common Shares Outstanding
Conversion of outstanding stock (in shares)			137,000
Share Purchase Agreement, Weichai Transaction | Common Stock
Common Shares Issued
Shares issued to Weichai (in shares)			4,050,000
Common Shares Outstanding
Shares issued to Weichai (in shares)			4,050,000
Share Purchase Agreement, Second Amended And Restated Warrant | Series B
Common Shares Outstanding
Warrants exercised (in shares)		4,049,759
Percent ownership of outstanding common stock	51.50%