SCHEDULE II. VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 11,800		$ 25,649		$ 15,119
Charged to Cost and Expenses	5,346		(38)		13,047
Due to Currency Translation Adjustments	533		(320)		(1,585)
Other	(12,948)	[1]	(13,491)		(932)
Balance at End of Period	4,731		11,800		25,649
Deferred Tax Assets - Valuation Allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	146,097		110,680		131,422
Charged to Cost and Expenses	33,041		38,490		13,175
Due to Currency Translation Adjustments	10,097		(6,323)		(11,519)
Other	(15,009)		3,250	[2]	(22,398)
Balance at End of Period	174,226		$ 146,097		110,680
Pension adjustments
Movement in Valuation Allowances and Reserves [Roll Forward]
Non-cash tax expense	(11,600)				(16,100)
US tax rate changes [Member] [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Non-cash tax expense	$ 4,600
UK tax rate changes
Movement in Valuation Allowances and Reserves [Roll Forward]
Non-cash tax expense					$ 6,300

[1] Includes the write-off of previously reserved accounts receivable balances.

[2] Includes a decrease of $11.6 million and $16.1 million for 2017 and 2015, respectively, related to pension adjustments recorded through Accumulated other comprehensive loss; and a $4.6 million decrease related to a U.S. tax rate change for 2017 and $6.3 million decrease related to a U.K. tax rate change for 2015.