Income Per Share (Summary of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income available to common unitholders	$ (40,039)	$ 38,522	$ 117,055	$ 101,728	$ (52,268)	$ 109,314	$ 41,510	$ 34,186	$ 217,266	$ 132,718	$ 271,583
Weighted average units outstanding—basic (in shares)									138,247,606	133,369,047	127,941,134
Stock options (in shares)									20,424	30,434	61,375
Unvested incentive units (in shares)									95,746	90,449	125,132
Market performance-based awards (in shares)									501,645	147,305	0
Weighted average units outstanding—diluted (in shares)									138,865,421	133,637,235	128,127,641
Basic (in dollars per share)	$ (0.28)	$ 0.28	$ 0.86	$ 0.75	$ (0.39)	$ 0.81	$ 0.31	$ 0.27	$ 1.57	$ 1.00	$ 2.12
Diluted (in dollars per share)	$ (0.28)	$ 0.28	$ 0.86	$ 0.75	$ (0.39)	$ 0.80	$ 0.31	$ 0.26	$ 1.56	$ 0.99	$ 2.12