Long-Term Incentive Plan Units (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	58 Months Ended			58 Months Ended	4 Months Ended	58 Months Ended		3 Months Ended		6 Months Ended		58 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Jun. 30, 2012 Directors [Member] Long-Term Incentive Plan Units [Member]	Dec. 31, 2007 Manager [Member] Long-Term Incentive Plan Units [Member]	Jun. 30, 2012 Manager [Member] Long-Term Incentive Plan Units [Member]	Jun. 30, 2012 Dedicated Personnel [Member] Long-Term Incentive Plan Units [Member]	Jun. 30, 2012 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Jun. 30, 2011 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Jun. 30, 2012 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Jun. 30, 2011 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Jun. 30, 2012 Non-Manager [Member] Long-Term Incentive Plan Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units granted				18,750	375,000		5,500
Expenses associated with LTIP unit awards								$ 0.03	$ 0.04	$ 0.06	$ 0.08	$ 0.50
Aggregate expense associated with Manager LTIP, Since inception						8.6
Vesting period (years)										one
Common shares issued in connection with conversion since inception	8,750
Amount transferred from share-based LTIP awards to Shareholders Equity	$ 0.2
Common shares issued and outstanding	16,838,151	16,838,151
Shareholders' equity per share upon conversion	$ 23.47	$ 22.03	$ 22.78