Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Supplemental cash flow information
Cash paid for interest	$ 4,380,000	$ 3,888,000
Supplemental schedule of non-cash investing and financing activities
Non cash investing activities included in additions of land and building improvements	(37,000)	285,000
Dividends and distributions declared but not paid	16,122,000	7,793,000	11,301,000
Restricted Cash
Amount held by the company's transfer agent for preferred stock dividends and distributed subsequent	$ 1,600,000