Net Income Per Limited Partner Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						6 Months Ended	9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Net income per limited partner unit
Net income	$ 119,764	$ 109,466	$ 108,105	$ 80,893	$ 87,176	$ 75,091		$ 337,335	$ 243,160
Net income attributable to incentive distribution rights	(37,816)			(19,067)				(99,414)	(45,948)
Limited partners' interest in net income	$ 81,948			$ 61,826				$ 237,921	$ 197,212
Net income per limited partner unit–basic	$ 0.44			$ 0.33				$ 1.27	$ 1.06
Weighted average limited partner units outstanding - basic	187,044,000			186,581,000				186,999,000	185,240,000
Weighted average limited partner units outstanding - diluted	187,502,000			187,145,000				187,342,000	185,728,000
Phantom share units
Net income per limited partner unit
Weighted average limited partner units outstanding - diluted	457,795						343,227
Restricted and phantom unit award
Net income per limited partner unit
Weighted average limited partner units outstanding - diluted							187,342,199
Weighted average units outstanding:
Antidilutive securities excluded from computation of earnings per share	0							0
Common units
Net income per limited partner unit
Weighted average limited partner units outstanding - diluted	187,501,733