Sales and Revenues - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Entity Wide Information Revenue From External Customer [Line Items]
Term used to calculate historical weighted average return rate	4 years
Estimated value of trucks to be returned	$ 364,400,000	$ 319,800,000
Estimated sales returned liabilites	376,600,000	329,300,000
Payment to acquire commitment value	781,800,000
Estimated value of returned goods	49,300,000	49,000,000.0
Sales returns liabilities in estimated returns	109,300,000	104,500,000
Financial Services
Entity Wide Information Revenue From External Customer [Line Items]
Total operating lease income	200,700,000
Financing receivable, recorded investment, 90 days past due and still accruing	0	$ 0
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total operating lease income	$ 41,700,000
Minimum
Entity Wide Information Revenue From External Customer [Line Items]
Lease and guarantee periods (in years)	3 years
Minimum | Financial Services
Entity Wide Information Revenue From External Customer [Line Items]
Operating lease term	3 years
Minimum | Trucks | Financial Services
Entity Wide Information Revenue From External Customer [Line Items]
Finance leases, lease term	3 years
Maximum
Entity Wide Information Revenue From External Customer [Line Items]
Lease and guarantee periods (in years)	5 years
Warranty period	5 years
Maximum | Financial Services
Entity Wide Information Revenue From External Customer [Line Items]
Operating lease term	5 years
Maximum | Trucks | Financial Services
Entity Wide Information Revenue From External Customer [Line Items]
Finance leases, lease term	5 years