Significant Accounting Policies Activity in Polaris Accrued Warranty Reserve (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Deferred tax liabilities	$ 7,054		$ 7,054		$ 10,128
Activity in Product Warranty Reserve [Roll Forward]
Balance at beginning of period	106,155	$ 108,403	123,840	$ 119,274
Additions to warranty reserve through acquisitions	13,799	0	13,799	0
Additions charged to expense	37,741	42,039	79,913	103,855
Warranty claims paid, net	(35,151)	(38,357)	(95,008)	(111,044)
Balance at end of period	$ 122,544	$ 112,085	$ 122,544	$ 112,085