Subsequent Events (Details) (USD $) In Thousands	6 Months Ended		1 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jul. 31, 2011 Issuance of debt
Subsequent Events
Number of common units issued through public offering (in units)	3,450		4,000
Net proceeds from issuance of common units after deducting underwriters fees and other third-party expenses	$ 138,163	$ 142,255	$ 185,100