Partners' Capital and Distributions Narrative (Details) (USD $)	3 Months Ended	9 Months Ended
	Mar. 31, 2012	Sep. 30, 2012	Sep. 30, 2011
Capital Unit [Line Items]
Equity Distribution Agreement maximum aggregate value of common units to be sold		$ 200,000,000
Common units issued under equity distribution program, net of costs		15,352,000	0
Common unit offering, net of costs		296,817,000	203,917,000
Repayments of long-term debt	$ 87,500,000	$ 87,500,000	$ 0
Common Unit Public Offering [Member]
Capital Unit [Line Items]
Partners' capital account, units, sold in public offering	12,650,000
Common issuance price per unit	$ 24.47
Senior note redeemable portion	35.00%
Common Stock [Member]
Capital Unit [Line Items]
Common units issued under equity distribution program, units		691,129