Distributions Paid and Payable (Details) (USD $)				3 Months Ended		1 Months Ended						3 Months Ended		1 Months Ended	3 Months Ended				12 Months Ended		0 Months Ended	1 Months Ended		3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Jan. 22, 2013 Tau Operating Partnership, L.P.	Mar. 31, 2013 ARCT Tau Operating Partnership, L.P. Common Units item	Mar. 31, 2013 ARCT Tau Operating Partnership, L.P. Preferred Unit item	Mar. 31, 2013 Common stock	Feb. 28, 2013 Common stock	Jan. 31, 2013 Common stock	Mar. 31, 2012 Common stock	Feb. 29, 2012 Common stock	Jan. 31, 2012 Common stock	Mar. 31, 2013 Common stock	Mar. 31, 2012 Common stock	Mar. 31, 2012 Class D Cumulative Redeemable Preferred Stock	Mar. 31, 2013 Class D Cumulative Redeemable Preferred Stock	Mar. 31, 2012 Class D Cumulative Redeemable Preferred Stock	Mar. 31, 2013 Class E Cumulative Redeemable Preferred Stock M	Mar. 31, 2012 Class E Cumulative Redeemable Preferred Stock M	Dec. 31, 2006 Class E Cumulative Redeemable Preferred Stock	Dec. 07, 2011 Class E Cumulative Redeemable Preferred Stock	Mar. 15, 2012 Class F Cumulative Redeemable Preferred Stock	Mar. 31, 2012 Class F Cumulative Redeemable Preferred Stock	Feb. 29, 2012 Class F Cumulative Redeemable Preferred Stock	Mar. 31, 2013 Class F Cumulative Redeemable Preferred Stock M	Apr. 30, 2012 Class F Cumulative Redeemable Preferred Stock
Distributions paid and payable
Dividends paid per common share (in dollars per share)						$ 0.1809167	$ 0.1809167	$ 0.1517500	$ 0.1455	$ 0.1455	$ 0.1455	$ 0.5135834	$ 0.4365
Monthly distributions payable (in dollars per share)						$ 0.1812292						$ 0.1812292					$ 0.140625							$ 0.138021
Units issued in connection with acquisition				317,022	6,750
Number of monthly distributions paid				2	2
Distributions paid per unit (in dollars per share)				$ 0.3618334
Distributions paid (in dollars)				$ 115,000	$ 20,000
Monthly distributions payable (in dollars per share)				$ 0.1812292
Payment rate per annum (as a percent)			2.00%		2.00%
Distributions payable (in dollars)					11,000
Preferred stock redeemed (in shares)														5,100,000
Preferred stock, dividend rate (as a percent)														7.375%	7.375%		6.75%	6.75%	6.75%				6.625%	6.625%
Dividends paid per preferred share (in dollars per share)																$ 0.3841147	$ 0.421875	$ 0.421875				$ 0.1702257		$ 0.414063
Preferred stock dividends paid																$ 2,000,000	$ 3,700,000	$ 3,700,000				$ 2,500,000		$ 6,800,000
Period for which dividends are paid																	3	3						3
Preferred stock, shares issued	25,150,000	25,150,000																	8,800,000				14,950,000		1,400,000
Preferred stock, redemption price per share (in dollars per share)	$ 25													$ 25		$ 25				$ 25				$ 25
Preferred stock, issuance price per share (in dollars per share)																			$ 25				$ 25		$ 25.2863
Period when initial dividend payments were made																					37 days