Asset-Backed Financing (Narrative) (Detail)	1 Months Ended	3 Months Ended									12 Months Ended
	Jun. 30, 2018 CAD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jul. 01, 2018 USD ($)	Apr. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 24, 2017 USD ($)	Jun. 25, 2017 USD ($)	Mar. 26, 2017 USD ($)	Jun. 26, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 30, 2018 USD ($)
Variable Interest Entity [Line Items]
Company issued secured notes, net of discount and issuance costs		$ 6,463,466,000				$ 5,714,527,000					$ 6,463,466,000	$ 5,714,527,000
Financial Services interest expense											193,187,000	180,193,000	$ 173,756,000
Servicing and ancillary fees											1,100,000	1,900,000
Secured Debt
Variable Interest Entity [Line Items]
Company issued secured notes, net of discount and issuance costs		$ 833,835,000				$ 806,860,000					833,835,000	806,860,000
Variable Interest Entity, Primary Beneficiary | Secured Debt
Variable Interest Entity [Line Items]
Financial Services interest expense											$ 3,200,000	$ 7,900,000
Weighted average interest rate at date of issuance		1.67%				1.53%					1.67%	1.53%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Secured Notes Issued January 2015
Variable Interest Entity [Line Items]
Company issued secured notes		$ 700,000,000									$ 700,000,000
Weighted average interest rate at date of issuance		0.89%									0.89%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Term asset-backed securitizations
Variable Interest Entity [Line Items]
Company issued secured notes		$ 500,000,000									$ 500,000,000
Weighted average interest rate at date of issuance		0.88%									0.88%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE | Line of Credit
Variable Interest Entity [Line Items]
Financial Services interest expense											$ 10,900,000	$ 7,100,000
Weighted average interest rate at date of issuance		3.26%									3.26%
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE | U.S. Line of Credit
Variable Interest Entity [Line Items]
Debt instrument, term											5 years
Transfers on finance receivables		$ 400,200,000	$ 0	$ 59,100,000	$ 32,900,000	$ 34,000,000	$ 34,100,000	$ 28,200,000	$ 333,400,000		$ 492,200,000	429,700,000
Amount transferred, face amount		356,800,000	0	53,300,000	29,300,000	$ 29,700,000	29,600,000	24,000,000	300,000,000		439,400,000	383,300,000
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE, Facility 1 | U.S. Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity														$ 600,000,000
Variable Interest Entity, Primary Beneficiary | Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE, Facility 2 | U.S. Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity														$ 300,000,000
Unconsolidated VIEs
Variable Interest Entity [Line Items]
Principal balance of finance receivable										$ 301,800,000
Gain on sale of finance receivable										9,300,000
Cash proceeds from sale of financial asset										$ 312,600,000
Unpaid principal balance of the retail motorcycle finance receivables		$ 79,600,000									79,600,000
Unconsolidated VIEs | Secured Debt | Asset-backed Canadian commercial paper conduit facility
Variable Interest Entity [Line Items]
Financial Services interest expense											$ 3,800,000	$ 2,600,000
Weighted average interest rate at date of issuance		2.68%				1.96%					2.68%	1.96%
Unconsolidated VIEs | Secured Debt | Asset-backed Canadian commercial paper conduit facility | Foreign Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity	$ 220,000,000
Debt instrument, term	5 years
Transfers on finance receivables		$ 39,000,000	0	38,900,000	7,600,000	$ 84,900,000	0	14,200,000	6,300,000		$ 85,500,000	$ 105,400,000
Amount transferred, face amount		32,200,000	$ 0	$ 32,200,000	$ 6,200,000	$ 69,100,000	$ 0	$ 12,400,000	$ 5,500,000		70,600,000	$ 87,000,000
VIE, maximum loss exposure, amount		$ 31,800,000									$ 31,800,000