Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2014
Issuance of common stock, shares	71,782
Pursuant to dividend reinvestment plan, shares	39,588
Exercise of employee stock options and issuance of directors' deferred stock, shares	32,194
Issuance of partnership units, shares	91,352
Distributions payable common stock, per share (in usd per share)	$ 0.40
Dividend Declared
Distributions payable common stock, per share (in usd per share)	$ 0.40
Distributions partnership units, per unit (in usd per unit)	$ 0.40
Dividend Declared | Series A Preferred Stock
Preferred stock, per share (in usd per share)	$ 50.00
Dividend Declared | Series C Preferred Stock
Preferred stock, per share (in usd per share)	$ 42.97