Summary of Significant Accounting Policies Earnings per Unit (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Basic weighted average units outstanding	55,476,000	55,518,000	55,345,000
Effect of dilutive units:
Unit options (Note 7)	162,000	43,000	0
Phantom units (Note 7)	187,000	334,000	541,000
Diluted weighted average units outstanding	55,825,000	55,895,000	55,886,000
Net income (loss) per unit - basic	1.95	1.83	1.18
Net income (loss) per unit - diluted	1.94	1.82	1.17
Unit Options [Member]
Effect of dilutive units:
Antidilutive securities excluded from computation of earnings per unit amount	5,300	11,600	63,000