Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	9 Months Ended
	Sep. 30, 2013
Issuance of common stock, shares	471,829
Pursuant to dividend reinvestment plan, shares	426,326
Exercise of employee stock options and issuance of directors' deferred stock, shares	45,503
Distributions payable common stock, per share (in usd per share)	$ 1.08
Series C Preferred Stock
Issuances of cumulative preferred stock, shares	56,000
Series A Preferred Stock
Redemption of Cumulative preferred stock, shares	24,000
Series B Preferred Stock
Redemption of Cumulative preferred stock, shares	31,731
Dividend Declared
Distributions payable common stock, per share (in usd per share)	$ 0.36
Distributions partnership units, per unit (in usd per unit)	$ 0.36
Dividend Declared | Series C Preferred Stock
Preferred stock, per share (in usd per share)	$ 42.97
Dividend Declared | Series A Preferred Stock
Preferred stock, per share (in usd per share)	$ 50.00