Asset-Backed Financing (Narrative) (Detail)	1 Months Ended				3 Months Ended						9 Months Ended
	Jul. 31, 2017 USD ($)	Apr. 30, 2017 USD ($)	Jan. 31, 2017 USD ($)	Jun. 30, 2016 CAD	Sep. 24, 2017 USD ($)	Jun. 25, 2017 USD ($)	Mar. 26, 2017 USD ($)	Sep. 25, 2016 USD ($)	Jun. 26, 2016 USD ($)	Mar. 27, 2016 USD ($)	Sep. 24, 2017 USD ($)	Sep. 25, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 14, 2016 USD ($)
Variable Interest Entity [Line Items]
Company issued secured notes, net of discount and issuance costs					$ 6,138,192,000			$ 5,870,761,000			$ 6,138,192,000	$ 5,870,761,000	$ 5,751,859,000
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Principal balance of finance receivable								301,800,000				301,800,000
Asset-backed securitization debt | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Principal balance of finance receivable								301,800,000				301,800,000
Gain on sale of finance receivable								9,300,000
Cash proceeds from sale of financial asset								312,600,000				312,600,000
Unpaid principal balance of the retail motorcycle finance receivables					165,200,000						165,200,000
Secured Debt
Variable Interest Entity [Line Items]
Company issued secured notes, net of discount and issuance costs					832,271,000			1,066,107,000			832,271,000	1,066,107,000	945,613,000
Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE [Member] | SPEs | U.S. Line of Credit
Variable Interest Entity [Line Items]
Company issued secured notes	$ 29,600,000	$ 24,000,000	$ 300,000,000
Line of credit, maximum borrowing capacity														$ 900,000,000
Transfers on finance receivables	$ 34,100,000	$ 28,200,000	$ 333,400,000
Borrowings outstanding under conduit facility								0				0	$ 0
Debt instrument, term	5 years	5 years	5 years
Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE, Facility Two [Member] | SPEs | U.S. Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity														300,000,000
Secured Debt | Asset-Backed U.S. Commercial Paper Conduit Facility VIE, Facility One [Member] | SPEs | U.S. Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity														$ 600,000,000
Secured Debt | Asset-backed Canadian commercial paper conduit facility | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Transfers on finance receivables					0	$ 14,200,000	$ 6,300,000	$ 0	$ 31,400,000	$ 6,600,000	20,500,000	$ 38,000,000
Secured Debt | Asset-backed Canadian commercial paper conduit facility | Variable Interest Entity, Not Primary Beneficiary | Foreign Line of Credit
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity | CAD				CAD 220,000,000
Debt instrument, term				5 years
VIE, maximum loss exposure, amount					$ 23,100,000						$ 23,100,000