Commitments And Contingencies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Cash and cash equivalents	$ 462,516	$ 370,853	$ 450,193	$ 385,235
Derivative, Amount of Hedged Item	200,000
Fair Value Hedge Liabilities	(878)		(1,557)
Other income (expense), net	(2,556)	(5,988)
Loans Payable to Bank	300,000		$ 300,000
Notes Payable, Fair Value Disclosure	500,000
Other Income [Member]
Loss Contingencies [Line Items]
Other income (expense), net	(500)	$ (7,000)
Angola, Kwanza
Loss Contingencies [Line Items]
Cash and cash equivalents	21,000
Angola [Member]
Loss Contingencies [Line Items]
Investments and Other Noncurrent Assets	58,928
Fair Value, Inputs, Level 2 [Member]
Loss Contingencies [Line Items]
Investments, Fair Value Disclosure	57,496
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Fair Value Hedge Liabilities	(1,389)
Other Noncurrent Assets [Member]
Loss Contingencies [Line Items]
Fair Value Hedge Assets	$ 500