Summary of Significant Accounting Policies Earnings per Unit (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic weighted average units outstanding	55,518,000	55,345,000	55,316,000
Effect of dilutive units:
Unit options (Note 7)	43,000	0	0
Phantom units (Note 7)	334,000	541,000	0
Diluted weighted average units outstanding	55,895,000	55,886,000	55,316,000
Net income (loss) per unit - basic	1.82	1.28	(0.6)
Net income (loss) per unit - diluted	1.81	1.27	(0.6)
Unit Options [Member]
Effect of dilutive units:
Antidilutive securities excluded from computation of earnings per unit amount	11,600	63,000	304,000