Stockholders' Equity of the Company (Details Textuals) - USD ($)		1 Months Ended				3 Months Ended		12 Months Ended
	Dec. 13, 2016	Jul. 31, 2015	Oct. 31, 2014	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 27, 2017	Feb. 23, 2016	Jul. 01, 2015	Oct. 01, 2014
Class of Stock [Line Items]
At market stock aggregate gross sales price of common stock										$ 300,000,000			$ 249,800,000
Common stock, shares issued													3,733,766
Shares issued, price per share													$ 66.19
Aggregate net proceeds after sales agent compensation		$ 249,600,000
Stock repurchase program, number of shares authorized to be repurchased												4,000,000
Stock repurchase program, remaining number of shares authorized to be repurchased						4,935,826		4,935,826				4,988,025
Stock repurchased during period, shares							52,199
Treasury stock acquired, average cost per share							$ 55.45
Stock repurchased during period, value							$ 2,900,000
Dividends declared per common share	$ 1.90					$ 0.375		$ 3.375	$ 1.4	$ 1.40
Common stock [Member]
Class of Stock [Line Items]
Common stock, shares issued						93,219,439		93,219,439	92,258,690
Dividends declared per common share						$ 2.275		$ 3.375	$ 1.400	$ 1.400
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividend rate (percentage)					6.875%			6.875%	6.875%
Preferred units, issued									4,000,000
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividend rate (percentage)				6.375%				6.375%	6.375%
Preferred units, issued									4,000,000
Issuance of Equity under ATM Program [Member] | Common stock [Member]
Class of Stock [Line Items]
At market stock aggregate gross sales price of common stock						$ 182,400,000		$ 182,400,000
Common stock, shares issued						2,459,165		2,459,165
At market stock offering program remained available for issuance						$ 117,600,000		$ 117,600,000
Aggregate net proceeds after sales agent compensation								$ 31,900,000	$ 138,200,000	$ 103,100,000
SFFGA [Member]
Class of Stock [Line Items]
Common stock, shares issued														351,476
Purchase price, value of shares issued to acquire land			$ 21,600,000
Series G Cumulative Redeemable Preferred Unit [Member] | Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred units, issued						4,000,000		4,000,000
Series H Cumulative Redeemable Preferred Unit [Member] | Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred units, issued						4,000,000		4,000,000
Scenario, forecast [Member] | Series G and H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, redemption price per share											$ 25.00
Preferred stock, redemption amount											$ 200,000,000.0
Preferred stock, redemption amount, potential charge											$ 7,600,000