Net Income Per Unit (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Earnings Per Share, Basic, by Common Class, Including Two Class Method
Net income attributable to partners													$ 56,791		$ 34,568		$ 0
Distributions less than (greater than) earnings													(7,876)		4,765
General partner's earnings:
General partner's distributions (including IDRs)													2,839		597
Allocation of distributions less than (greater than) earnings													(155)		95
Total general partner's earnings													2,684		692
Limited partners' earnings on common units:
Limited partners' distributions on common units													35,666		14,603
Allocation of distributions less than (greater than) earnings													(4,025)		2,335
Total limited partners' earnings on common units													31,641		16,938
Limited partner's earnings on subordinated units:
Limited partner's distributions on subordinated units													26,162		14,603
Allocation of distributions less than (greater than) earnings													(3,696)		2,335
Total limited partner's earnings on subordinated units													22,466		16,938
Weighted average limited partner units outstanding:
Common units - basic (units)													16,614,668		15,254,890
Common unit equivalents (units)													94,282		27,476
Common units - diluted (units)													16,708,950		15,282,366
Subordinated units - basic and diluted (units)													15,254,890		15,254,890
Net income per limited partner unit:
Common - basic (dollars per unit)	$ 0.53	$ 0.55	$ 0.41	$ 0.37									$ 1.90		$ 1.11
Common - diluted (dollars per unit)	$ 0.53	$ 0.54	$ 0.41	$ 0.37									$ 1.89		$ 1.11
Subordinated - basic and diluted (dollars per unit)	$ 0.30	$ 0.41	$ 0.41	$ 0.37	$ 0.37	[1]	$ 0.49	[1]	$ 0.25	[1]	$ 0.00	[1]	$ 1.47		$ 1.11	[1]
Footnote
General partner's ownership interest													2.00%		2.00%
Maximum percentage distribution to general partner													50.00%
Minimum distribution level for IDRs													0.388125
General Partner
Earnings Per Share, Basic, by Common Class, Including Two Class Method
Net income attributable to partners													2,674		692
Distributions													2,839	[2]	597	[2]
Common
Earnings Per Share, Basic, by Common Class, Including Two Class Method
Net income attributable to partners													28,238		16,938
Distributions													35,666		14,603
Subordinated
Earnings Per Share, Basic, by Common Class, Including Two Class Method
Net income attributable to partners													25,879		16,938
Distributions													$ 26,162		$ 14,603

[1] Net income per unit is only calculated for the Partnership after the Initial Offering as no units were outstanding prior to April 26, 2011.

[2] General partner's distributions (including IDRs) consist of the 2% general partner interest and IDRs, which entitle the general partner to receive increasing percentages, up to 50%, of quarterly distributions in excess of $0.388125 per unit per quarter. See Note L for further discussion related to IDRs.