Common Stock (Details) (USD $)	0 Months Ended	3 Months Ended					3 Months Ended			3 Months Ended			0 Months Ended				3 Months Ended
	Mar. 08, 2013	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Aug. 01, 2012	Mar. 31, 2013 Common Stock [Member]	Mar. 31, 2013 ARCP [Member]	Mar. 31, 2013 Follow on Offering [Member]	Jan. 28, 2013 Follow on Offering [Member]	Mar. 31, 2013 At the Market Offering [Member]	Apr. 30, 2013 At the Market Offering [Member]	Mar. 31, 2013 Registration Payment Arrangement, Arrangement [Domain]	Feb. 28, 2013 ARCP Merger [Member] ARCP [Member]	Feb. 28, 2013 Cash [Member] Option Two [Member] ARCP Merger [Member]	Feb. 28, 2013 Cash [Member] Option Two [Member] ARCP shares converted from ARCT III shares [Member]	Feb. 28, 2013 Common Stock [Member] Option One [Member] ARCP Merger [Member]	Mar. 31, 2013 Common Stock	Dec. 31, 2012 Common Stock
Class of Stock [Line Items]
Shares, Issued						0
Common Stock, Dividend Rate, Per Share		$ 0.900
Common stock, shares authorized		240,000,000		240,000,000								1,882,248
Common stock, issued		154,322,183		179,167,112		2,131,000			2,070,000	61,000	492,300					140,700,000
Proceeds from issuances of common stock		$ 27,543,000	$ 184,811,000				$ 27,500,000	$ 0		$ 800,000
Share of Common Stock													0.95
Dividends declared, in dollars per share	$ 0.9100
Shares, Outstanding														29,200,000	27,700,000	148,113,788.5	154,322,183	179,167,112
Convertible stock issued during period, value														$ 12.00
Maximum Amount of Offering from Universal Shelf Registration Statement					$ 500,000,000					$ 60,000,000
Shares Issued (in shares)																	2,100,000