Product warranties (Provision for warranty obligations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Product Warranties Disclosures [Abstract]
Product warranty period, maximum	50 years
Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 32,930	$ 30,144	$ 37,265
Acquisitions	3,389	0	0
Warranty claims paid during the period	(52,011)	(55,314)	(57,163)
Pre-existing warranty accrual adjustment during the period	0	0	4,473
Warranty expense during the period	51,510	58,100	45,569
Balance at end of period	$ 35,818	$ 32,930	$ 30,144