Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets associated with interest rate swap and foreign currency forward contracts	$ 15,621	$ 14,137
Liabilities associated with interest rate swap and foreign currency forward contracts	(10,861)	(30,989)
Acquisition-related contingent consideration
Liabilities associated with acquisition-related contingent consideration	(42,614)
Additions to asset retirement obligations liability
Total additional asset retirement obligations incurred for the period	11,727	8,720
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets associated with interest rate swap and foreign currency forward contracts	15,621	14,137
Liabilities associated with interest rate swap and foreign currency forward contracts	(10,861)	(30,989)
Level 3
Acquisition-related contingent consideration
Liabilities associated with acquisition-related contingent consideration	(42,614)
Additions to asset retirement obligations liability
Total additional asset retirement obligations incurred for the period	11,700	$ 8,700
Foreign Exchange Forward [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities associated with interest rate swap and foreign currency forward contracts	(100)
Senior Notes 5.125 Percent Due 2022 | Level 2 [Member]
Long-term debt
Fair value of long term notes	240,000
Convertible Senior Notes 1.00 percent due 2020 | Level 2 [Member]
Long-term debt
Fair value of long term notes	257,800
Senior Notes 5.50 Percent Due 2025 | Level 2 [Member]
Long-term debt
Fair value of long term notes	$ 272,300