Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	6 Months Ended
	Jun. 30, 2013
Issuance of common stock, shares	307,587
Pursuant to dividend reinvestment plan, shares	288,307
Exercise of employee stock options and issuance of directors' deferred stock, shares	19,280
Series C Preferred Stock
Issuances of cumulative preferred stock, shares	56,000
Series A Preferred Stock
Redemption of Cumulative preferred stock, share	24,000
Series B Preferred Stock
Redemption of Cumulative preferred stock, share	31,731
Dividend Declared
Distributions payable common stock, per share	$ 0.36
Distributions partnership units, per unit	$ 0.36
Dividend Declared | Series C Preferred Stock
Preferred stock, per share	$ 42.97
Dividend Declared | Series A Preferred Stock
Preferred stock, per share	$ 50.00