Debt - Narrative (Details)			3 Months Ended	6 Months Ended
	May 20, 2024 USD ($)	Mar. 22, 2024 USD ($) agreement	Jun. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jun. 30, 2023 USD ($)	Dec. 10, 2021 USD ($)
Debt Instrument [Line Items]
Debt issuance costs			$ 100,000	$ 100,000	$ 200,000
Short-term financing			134,820,000	134,820,000	144,820,000
Number of amended agreements | agreement		1
Number of agreements | agreement		4
Debt, long-term and short-term, combined amount			135,100,000	135,100,000	145,200,000
Cash and cash equivalents			28,801,000	28,801,000	22,758,000	$ 27,782,000
Accrued unpaid interest			2,300,000	2,300,000	1,900,000
$25 Million Loan Agreement
Debt Instrument [Line Items]
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) [Member]
Basis spread on variable rate (as percent)	4.05%
Revolving Credit Facility | First Shareholder's Loan Agreement, Weichai
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 130,000,000.0
Revolving Credit Facility | First Shareholder's Loan Agreement, Weichai - Amendment
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 50,000,000
Revolving Credit Facility | Third Amended And Restated Credit Agreement
Debt Instrument [Line Items]
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]		Secured Overnight Financing Rate (SOFR) [Member]
Basis spread on variable rate (as percent)		3.45%
Debt issuance costs		$ 100,000
Paydown related to credit agreement			5,000,000.0
Proceeds related to credit agreement			0
Short-term financing			40,000,000	$ 40,000,000	50,000,000
Revolving Credit Facility | $30 Million, $25 Million, and $50 Million Loan Agreements
Debt Instrument [Line Items]
Debt instrument, incremental borrowing cost (as percent)				1.00%
Revolving Credit Facility | $30 Million Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity			30,000,000.0	$ 30,000,000.0
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]				Secured Overnight Financing Rate (SOFR) [Member]
Basis spread on variable rate (as percent)				4.05%
Short-term financing			19,820,000	$ 19,820,000	19,820,000
Debt instrument, face amount		$ 30,000,000
Revolving Credit Facility | $25 Million Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity			25,000,000	25,000,000
Short-term financing			25,000,000	25,000,000	25,000,000
Debt instrument, face amount	$ 25,000,000
Revolving Credit Facility | $50 Million Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity			50,000,000	$ 50,000,000
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]				Secured Overnight Financing Rate (SOFR) [Member]
Basis spread on variable rate (as percent)				4.65%
Short-term financing			$ 50,000,000	$ 50,000,000	$ 50,000,000
Debt instrument, face amount							$ 50,000,000