Segment Information - By Geographic Area (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) customer	Dec. 31, 2016 USD ($) customer	Dec. 31, 2015 USD ($) customer
Financial information with respect to entity's operations by geographic area
Operating revenues	$ 708,277	$ 662,103	$ 631,355	$ 562,550	$ 538,948	$ 519,729	$ 571,591	$ 597,571	$ 2,564,285	$ 2,227,839	$ 3,864,437
Property, Plant and Equipment, Net	6,109,565				6,267,583				6,109,565	6,267,583	7,027,802
Goodwill	173,226				166,917				$ 173,226	$ 166,917	$ 166,659
Sales Revenue | One customer
Financial information with respect to entity's operations by geographic area
Number of customers | customer									1	1	1
Sales Revenue | Customer Concentration Risk | One customer
Financial information with respect to entity's operations by geographic area
Percentage									29.00%	33.00%	12.00%
United States
Financial information with respect to entity's operations by geographic area
Operating revenues									$ 973,464	$ 642,835	$ 1,823,906
Property, Plant and Equipment, Net	3,163,425				3,048,749				3,163,425	3,048,749	3,703,533
Goodwill	54,198				54,199				54,198	54,199	54,198
Outside the U.S
Financial information with respect to entity's operations by geographic area
Operating revenues									1,590,821	1,585,004	2,040,531
Property, Plant and Equipment, Net	2,946,140				3,218,834				2,946,140	3,218,834	3,324,269
Goodwill	$ 119,028				$ 112,718				119,028	112,718	112,461
Saudi Arabia
Financial information with respect to entity's operations by geographic area
Operating revenues									$ 727,700	$ 731,400	$ 604,500