Other Data (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2013
Other Data (Textual) [Abstract]
Condition to qualify as a REIT as defined under the Internal Revenue Code	Company must meet a number of organizational and operational requirements, including a requirement that it currently distribute at least 90% of its taxable income to its stockholders.
Estimated aggregate total cost of total assets for federal income tax purposes	$ 3,300,000,000	$ 2,800,000,000	$ 3,100,000,000
Number of preferred shares outstanding	0	0	0
Dividends distributed to preferred shares	0
Income tax expense	$ 100,000	$ 100,000