Basis of Presentation and Summary of Significant Accounting Policies (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	Jun. 30, 2013 Carrying Amount	Dec. 31, 2012 Carrying Amount	Jun. 30, 2013 Carrying Amount Fixed rate debt	Jun. 30, 2013 Carrying Amount Floating rate debt	Dec. 31, 2012 Carrying Amount Floating rate debt	Jun. 30, 2013 Fair Value	Dec. 31, 2012 Fair Value	Jun. 30, 2013 Fair Value Fixed rate debt	Jun. 30, 2013 Fair Value Floating rate debt	Dec. 31, 2012 Fair Value Floating rate debt
Financial Instruments
Total debt					$ 714,682	$ 680,500	$ 344,682	$ 370,000	$ 680,500	$ 716,000	$ 691,000	$ 345,000	$ 371,000	$ 691,000
Potential common units included in computing the dilutive potential common units used in dilutive earnings (loss) per common unit
Weighted average common units outstanding - used in basic earnings (loss) per common unit (in units)	49,409	42,264	45,863	40,467
Net dilutive potential common units issuable:
Phantom units (in units)	15		11
Weighted average common units and dilutive potential common units - used in diluted earnings (loss) per common unit (in units)	49,424	42,264	45,874	40,467