Accounts Receivable and Inventories (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Accounts receivable
Trade accounts receivable	$ 652,013		$ 652,013		$ 617,517
Less: Allowance for doubtful accounts	(20,058)		(20,058)		(17,253)
Trade accounts receivable, net	631,955		631,955		600,264
Other receivables	41,659		41,659		39,836
Provision for doubtful accounts related to trade accounts receivable	2,621	3,936	4,838	6,863
Inventories
Finished goods	79,282		79,282		69,904
Work-in-process	36,834		36,834		28,944
Raw materials and purchased parts	91,276		91,276		99,058
Stores and supplies	37,444		37,444		38,606
Inventories	$ 244,836		$ 244,836		$ 236,512