Accrued Warranty Costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Product warranty obligation
Balance at beginning of period	$ 6,078	$ 4,598	$ 5,370	$ 3,996
Amounts charged to costs and expenses	1,718	1,636	5,062	4,870
Costs incurred	(1,720)	(1,241)	(4,356)	(3,873)
Balance at end of period	$ 6,076	$ 4,993	$ 6,076	$ 4,993