Consolidated Statement of Stockholders' Equity (Unaudited) (Parenthetical)	9 Months Ended
	Sep. 30, 2015 $ / shares shares
Issuance of stock, shares | shares	230,621
Pursuant to dividend reinvestment plan, shares | shares	153,897
Exercise of employee stock options and issuance of directors' deferred stock, shares | shares	76,724
Issuance of partnership units, shares | shares	78,101
Distributions payable common stock, per share (in usd per share)	$ 1.29
Dividend Distributions Payable
Distributions payable common stock, per share (in usd per share)	0.43
Distributions partnership units, per unit (in usd per unit)	0.43
Series C Preferred Stock | Dividend Distributions Payable
Preferred stock, per share (in usd per share)	$ 42.97