Significant Accounting Policies Activity in Polaris Accrued Warranty Reserve (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Activity in Product Warranty Reserve [Roll Forward]
Balance at beginning of period	$ 123,840	$ 119,274
Additions charged to expense	16,031	31,694
Warranty claims paid, net	(23,585)	(41,116)
Balance at end of period	$ 116,286	$ 109,852
Off Road Vehicle
Product Warranty Liability [Line Items]
Period of warranties provided by Polaris	6 months