Commitments And Contingencies - Other Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies
Asset retirement obligations	$ 54,907	$ 54,727	$ 55,136
Purchase Commitment, Remaining Minimum Amount Committed	$ 16,800
Minimum service requirements
Commitments and Contingencies
Purchase commitment remaining period	3 years
Purchase Commitment, Remaining Minimum Amount Committed	$ 4,300