Summary of Significant Accounting Policies and Other Information - Narrative (Details)				1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 20, 2022 USD ($)	Mar. 25, 2022 USD ($) agreement day	Dec. 10, 2021 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2022 USD ($) boardMember $ / shares	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) boardMember segment $ / shares	Dec. 31, 2021 USD ($) $ / shares	Apr. 30, 2019 $ / shares
Concentration Risk [Line Items]
Common stock, par value (in dollars per share) | $ / shares					$ 0.001		$ 0.001	$ 0.001	$ 0.001
Number of board members | boardMember					4		4
Short-term financing					$ 209,820,000		$ 209,820,000	$ 155,000,000
Debt instrument, number of loan agreements amended | agreement		2
Debt, long-term and short-term, combined amount					210,600,000		210,600,000
Cash and cash equivalents					3,448,000	$ 5,503,000	$ 3,448,000	6,255,000
Number of operating segments | segment							1
Research and development and engineering expenses					4,500,000	6,100,000
Outstanding letters of credit amount					2,100,000		$ 2,100,000	2,100,000
Restricted cash					3,450,000	$ 2,949,000	3,450,000	3,477,000
Restricted cash recorded as liability					3,654,000		3,654,000	3,330,000
Specific warranty-related matter accrual					2,000,000		2,000,000
Revolving credit facility
Concentration Risk [Line Items]
Short-term financing					130,000,000		130,000,000	$ 130,000,000
Contract With Customer
Concentration Risk [Line Items]
Restricted cash					1,000,000.0		1,000,000.0
Restricted cash recorded as liability					1,400,000		1,400,000
Share Purchase Agreement, Weichai Transaction
Concentration Risk [Line Items]
Consideration received on transaction				$ 60,000,000.0
First, Second, And Fourth Shareholder's Loan Agreement, Weichai
Concentration Risk [Line Items]
Debt instrument, incremental borrowing cost	1.00%
First, Second, And Fourth Shareholder's Loan Agreement, Weichai | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Concentration Risk [Line Items]
Basis spread on variable rate	4.65%
First Shareholder's Loan Agreement, Weichai | Revolving credit facility
Concentration Risk [Line Items]
Short-term financing					0		0
Second Shareholder's Loan Agreement, Weichai | Revolving credit facility
Concentration Risk [Line Items]
Short-term financing					25,000,000		25,000,000
Fourth Shareholder's Loan Agreement, Weichai | Revolving credit facility
Concentration Risk [Line Items]
Short-term financing					4,800,000		4,800,000
Third Shareholder's Loan Agreement, Weichai | Revolving credit facility
Concentration Risk [Line Items]
Short-term financing					50,000,000		50,000,000
Revolving credit facility | Second Standard Chartered Bank Credit Agreement
Concentration Risk [Line Items]
Maximum borrowing capacity		$ 130,000,000
Number of days to submit borrowing request | day		5
Short-term financing					130,000,000		130,000,000
Basis spread on variable rate		2.95%
Revolving credit facility | First Shareholder's Loan Agreement, Weichai
Concentration Risk [Line Items]
Maximum borrowing capacity		$ 130,000,000			130,000,000		130,000,000
Revolving credit facility | Second Shareholder's Loan Agreement, Weichai
Concentration Risk [Line Items]
Maximum borrowing capacity		$ 25,000,000			25,000,000		25,000,000
Revolving credit facility | Fourth Shareholder's Loan Agreement, Weichai
Concentration Risk [Line Items]
Maximum borrowing capacity	$ 30,000,000				30,000,000		30,000,000
Revolving credit facility | Third Shareholder's Loan Agreement, Weichai
Concentration Risk [Line Items]
Maximum borrowing capacity			$ 50,000,000		$ 50,000,000		$ 50,000,000
Revolving credit facility | Third Shareholder's Loan Agreement, Weichai | LIBOR
Concentration Risk [Line Items]
Basis spread on variable rate			4.50%