Warranty Liability (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Warranty liability
Period of warranty history used in estimating warranty costs	5 years
Company's warranty liability:
Balance at the beginning of the period	$ 4,188	$ 3,399	$ 3,040
Warranty provision	846	3,386	2,604
Claims paid/settlements	(1,406)	(2,597)	(2,245)
Balance at the end of the period	$ 3,628	$ 4,188	$ 3,399
Snow and ice control equipment
Warranty liability
Warranty period	2 years
Parts and accessories
Warranty liability
Warranty period	1 year
Certain snowplows
Warranty liability
Warranty period	1 year