Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Income taxes (net of refunds of $17,522, $9,270 and $7,333 in 2017, 2016 and 2015, respectively)	$ 320,222	$ 143,404	$ 162,408
Income taxes, refunds	17,522	9,270	7,333
Interest (net of capitalization)	61,243	96,948	153,271
Capital expenditures included in Accounts payable	$ 89,188	$ 33,622	$ 45,826