Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) (USD $)	9 Months Ended
	Sep. 30, 2014
Issuance of stock, shares	293,387
Pursuant to dividend reinvestment plan, shares	157,496
Exercise of employee stock options and issuance of directors' deferred stock, shares	135,891
Issuance of partnership units, shares	196,183
Distributions payable common stock, per share (in usd per share)	$ 1.20
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
Series A Preferred Stock | Dividend Declared
Preferred stock, per share (in usd per share)	$ 50.00
Series C Preferred Stock | Dividend Declared
Preferred stock, per share (in usd per share)	$ 42.97