Equity, Equity Activity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Increase (Decrease) in Partners' Capital
Balance at December 31, 2012			$ (18,123)
Allocation of net assets acquired by the unitholders			399,023
Equity offering, net of issuance costs			399,899
Quarterly distributions			(46,904)
Distributions to unitholders and general partner related to acquisitions			(544,000)
Net income attributable to partners	19,173	13,085	37,851	24,641
Other			4,329
Balance at June 30, 2013	232,075		232,075
Common
Increase (Decrease) in Partners' Capital
Balance at December 31, 2012			153,037
Allocation of net assets acquired by the unitholders			391,043
Equity offering, net of issuance costs			397,169
Quarterly distributions			(29,155)
Distributions to unitholders and general partner related to acquisitions			(533,120)
Net income attributable to partners			22,732
Other			3,986
Balance at June 30, 2013	405,692		405,692
Subordinated
Increase (Decrease) in Partners' Capital
Balance at December 31, 2012			(144,162)
Allocation of net assets acquired by the unitholders			0
Equity offering, net of issuance costs			(5,268)
Quarterly distributions			(14,683)
Distributions to unitholders and general partner related to acquisitions			0
Net income attributable to partners			11,605
Other			195
Balance at June 30, 2013	(152,313)		(152,313)
General partner
Increase (Decrease) in Partners' Capital
Balance at December 31, 2012			(26,998)
Allocation of net assets acquired by the unitholders			7,980
Equity offering, net of issuance costs			7,998
Quarterly distributions			(3,066)
Distributions to unitholders and general partner related to acquisitions			(10,880)
Net income attributable to partners			3,514
Other			148
Balance at June 30, 2013	$ (21,304)		$ (21,304)