Contingencies (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Changes in Corporation's accruals for estimated product warranties
Balance at beginning of period	$ 3,107	$ 2,798	$ 2,574	$ 3,064
Acquired liabilities for warranties	609		609
Liabilities accrued for warranties issued during the period	853	404	2,444	1,141
Warranty claims paid during the period	(1,595)	(453)	(2,577)	(1,471)
Changes in liability for pre-existing warranties during the period, including expirations	14	10	(62)	25
Balance at end of period	$ 2,988	$ 2,759	$ 2,988	$ 2,759