Debt - Revolving Credit and Term Loan Agreement - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) Installment	Dec. 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Letters of credit	$ 0
Swing Line sub-facility [Member]
Line of Credit Facility [Line Items]
Interest accrued percentage		4.10%
Borrowed under the credit facility	0	$ 400,000
Letters of credit		$ 0
$60,000,000 Revolving Credit and Term Loan Agreement [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 60,000,000
Credit facility, expiration date	Dec. 23, 2020
Line of credit facility, interest rate description	The applicable margin fluctuates based on Westport’s total debt to EBITDA ratio, as defined in the Credit Agreement.
Credit facility, Interest Rates	LIBOR
Borrowed under the credit facility	$ 6,800,000
Letters of credit	0
Debt instrument, carrying amount	$ 11,800,000
Repayments of borrowings under term loan and revolving credit facility	50% (which percentage shall be reduced to 0% subject to Westport attaining a certain leverage ratio) of Westport’s annual excess cash flow, as defined; 100% of the net cash proceeds if we sell Westport’s machining division; 50% of net proceeds from certain equity issuances; 100% of proceeds from the issuance of certain indebtedness; and 100% of net proceeds from the sale of certain assets, insurance and condemnation proceeds.
Debt instrument, covenant term	The Credit Agreement includes financial covenants requiring Westport to maintain a minimum fixed charge coverage ratio, minimum quarterly EBITDA amounts, as defined in the Credit Agreement, and a maximum debt to EBITDA ratio, as well as customary affirmative and negative covenants and events of default. At December 31, 2015, we were in compliance with the debt covenants.
Equity interest in Westport	100.00%
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Rate management agreement [Member]
Line of Credit Facility [Line Items]
Notional amount	$ 12,000,000
Duration of agreement	2 years
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Net eligible accounts receivable [Member]
Line of Credit Facility [Line Items]
Credit facility, secured by asset	$ 17,600,000
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Inventory [Member]
Line of Credit Facility [Line Items]
Credit facility, secured by asset	$ 7,100,000
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Facility fee	0.25%
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Facility fee	0.50%
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 20,000,000
Line of credit facility, first quarterly interest payment commencement date	Mar. 01, 2016
Line of credit facility, frequency of payment term	Interest on the unpaid balance of all revolving credit facility and swing line base rate advances is payable quarterly in arrears commencing on March 1, 2016, and on the first day of each June, September, December and March thereafter. Interest on the unpaid balance of each Eurodollar-based advance of the revolving credit facility is payable on the last day of the applicable Eurodollar interest period. Interest on the unpaid balance of each quoted rate based advance of the swing line is payable on the last day of the applicable quoted rate interest period.
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Swing Line sub-facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity	$ 4,000,000
Borrowed under the credit facility	0
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Letter Of Credit
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity	2,000,000
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 40,000,000
Credit facility, expiration date	Dec. 23, 2020
Number of installments | Installment	20
Frequency of installments	Quarterly
Term loan installment amount	$ 1,500,000
Debt Instrument, term	5 years
Debt instrument, first quarterly interest payment commencement date	Jan. 01, 2016
Debt instrument, frequency of payment term	Interest on the unpaid principal of all term loan base rate advances is payable quarterly in arrears commencing on January 1, 2016, and on the first day of each April, July, October and January thereafter. Interest on the unpaid principal of each Eurodollar-based advance of the term loan is payable on the last day of the applicable Eurodollar interest period.
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | Term Loan [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Interest accrued percentage	2.92%
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | $6.0 million LIBOR rate advance [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 6,000,000
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | $6.0 million LIBOR rate advance [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Interest accrued percentage	2.42%
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | $5.8 million base rate advance [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 5,800,000
$60,000,000 Revolving Credit and Term Loan Agreement [Member] | $5.8 million base rate advance [Member] | Prime [Member]
Line of Credit Facility [Line Items]
Interest accrued percentage	4.50%