Accounts Receivable and Inventories (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Accounts receivable
Trade accounts receivable	$ 268,716		$ 280,526
Less: Allowance for doubtful accounts	(16,056)		(25,649)
Trade accounts receivable, net	252,660		254,877
Other receivables	19,458		30,395
Provision for doubtful accounts related to trade accounts receivable	(146)	$ 196
Inventories
Finished goods	35,694		32,586
Work-in-process	98,500		86,745
Raw materials and purchased parts	73,215		70,755
Stores and supplies	25,926		26,881
Inventories	$ 233,335		$ 216,967