Acquisitions (Schedule of Pro Forma Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Enterprise Offshore Acquisition [Member]
Pro forma earnings data:
Revenues from continuing operations	$ 2,421,989	$ 4,135,964
Net income	$ 425,363	$ 132,682
Basic and diluted earnings per unit:
As reported net income per unit (in dollars per share)	$ 4.09	$ 1.18
Pro forma net income per unit (in dollars per share)	$ 3.91	$ 1.32
M/T American Phoenix Acquisition [Member]
Pro forma earnings data:
Revenues from continuing operations		$ 3,863,745
Net income		$ 111,132