Transactions With Related Parties (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009
Related Party Transaction [Line Items]
Number of independent directors									4
Management Agreement additional term of expiration (in years)									1
Proportion of average annual management fee									3
Prior notice for uncertain termination (in days)									180
Period of annual management fees earned (in years)									2
Management fee amount determination									management fee payable monthly in arrears in an amount equal to 1/12th
Management fee	$ 3,592,000	$ 3,572,000	$ 3,531,000	$ 3,092,000	$ 2,505,000	$ 2,321,000	$ 2,196,000	$ 2,183,000	$ 13,787,000	$ 9,205,000	$ 8,677,000
Share based compensation expense	415,000	334,000	194,000	207,000	279,000	463,000	347,000	342,000	1,150,000	1,432,000	1,296,000
Management fee payable	1,200,000				828,000				1,200,000	828,000
Company's Equity Up To $250 Million [Member]
Related Party Transaction [Line Items]
Management fee percentage per annum									1.50%
Company's Equity In Excess Of $250 Million And Up To $500 Million [Member]
Related Party Transaction [Line Items]
Management fee percentage per annum									1.10%
Company's Equity In Excess Of $500 Million And Up To $750 Million [Member]
Related Party Transaction [Line Items]
Management fee percentage per annum									0.80%
Company's Equity In Excess Of $750 [Member]
Related Party Transaction [Line Items]
Management fee percentage per annum									0.50%
Minimum [Member] | Company's Equity In Excess Of $250 Million And Up To $500 Million [Member]
Related Party Transaction [Line Items]
Management fee bases									250,000,000
Minimum [Member] | Company's Equity In Excess Of $500 Million And Up To $750 Million [Member]
Related Party Transaction [Line Items]
Management fee bases									500,000,000
Minimum [Member] | Company's Equity In Excess Of $750 [Member]
Related Party Transaction [Line Items]
Management fee bases									750,000,000
Maximum [Member] | Company's Equity Up To $250 Million [Member]
Related Party Transaction [Line Items]
Management fee bases									250,000,000
Maximum [Member] | Company's Equity In Excess Of $250 Million And Up To $500 Million [Member]
Related Party Transaction [Line Items]
Management fee bases									500,000,000
Maximum [Member] | Company's Equity In Excess Of $500 Million And Up To $750 Million [Member]
Related Party Transaction [Line Items]
Management fee bases									$ 750,000,000