Segment Information - By Geographic Area (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) customer	Dec. 31, 2015 USD ($) customer	Dec. 31, 2014 USD ($)
Financial information with respect to entity's operations by geographic area
Operating revenues	$ 538,948	$ 519,729	$ 571,591	$ 597,571	$ 738,872	$ 847,553	$ 863,305	$ 1,414,707	$ 2,227,839	$ 3,864,437	$ 6,804,197
Property, Plant and Equipment, Net	6,267,583				7,027,802				6,267,583	7,027,802	8,599,125
Goodwill	166,917				166,659				$ 166,917	$ 166,659	173,928
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | One customer
Financial information with respect to entity's operations by geographic area
Number of customers | customer									1	1
Percentage									33.00%	12.00%
United States
Financial information with respect to entity's operations by geographic area
Operating revenues									$ 642,835	$ 1,823,906	4,701,122
Property, Plant and Equipment, Net	3,048,749				3,703,533				3,048,749	3,703,533	5,205,296
Goodwill	54,199				54,198				54,199	54,198	146,310
Outside the U.S
Financial information with respect to entity's operations by geographic area
Operating revenues									1,585,004	2,040,531	2,103,075
Property, Plant and Equipment, Net	3,218,834				3,324,269				3,218,834	3,324,269	3,393,829
Goodwill	$ 112,718				$ 112,461				$ 112,718	$ 112,461	$ 27,618