Long-Term Incentive Plan Units (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		61 Months Ended		61 Months Ended	0 Months Ended	4 Months Ended	61 Months Ended		3 Months Ended		9 Months Ended		61 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Directors [Member] Long-Term Incentive Plan Units [Member]	Sep. 12, 2012 Independent Directors [Member] Long-Term Incentive Plan Units [Member]	Dec. 31, 2007 Manager [Member] Long-Term Incentive Plan Units [Member]	Sep. 30, 2012 Manager [Member] Long-Term Incentive Plan Units [Member]	Sep. 30, 2012 Dedicated Personnel [Member] Long-Term Incentive Plan Units [Member]	Sep. 30, 2012 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Sep. 30, 2011 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Sep. 30, 2012 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Sep. 30, 2011 Non-Manager [Member] Long-Term Incentive Plan Units [Member]	Sep. 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							24,096	5,346	375,000		5,500
Expenses associated with LTIP unit awards	$ 31,000	$ 41,000	$ 89,000	$ 116,000								$ 30,000	$ 40,000	$ 90,000	$ 120,000	$ 500,000
Aggregate expense associated with Manager LTIP, Since inception										8,600,000
Vesting period (years)														1 year
Common shares issued in connection with conversion since inception					8,750
Amount transferred from share-based LTIP awards to Shareholders Equity					$ 200,000
Common shares issued and outstanding	20,879,542		20,879,542		20,879,542	16,838,151
Shareholders' equity per share upon conversion	$ 23.88	$ 22.32	$ 23.88	$ 22.32	$ 23.88	$ 22.03