Common Stock (Details) (USD $)	0 Months Ended	3 Months Ended	6 Months Ended						6 Months Ended			6 Months Ended			0 Months Ended			6 Months Ended		6 Months Ended
	May 28, 2013	Jun. 30, 2013	Jun. 30, 2013	Jun. 30, 2012	Jul. 02, 2013	Dec. 31, 2012	Aug. 01, 2012	Jun. 30, 2013 Common Stock [Member]	Jun. 30, 2013 ARCP [Member]	Jun. 30, 2013 Follow on Offering [Member]	Jan. 28, 2013 Follow on Offering [Member]	Jun. 30, 2013 At the Market Offering [Member]	Jun. 30, 2013 Private Placement [Member]	Jun. 30, 2013 Registration Payment Arrangement, Arrangement [Domain]	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]	Jun. 30, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Jun. 30, 2013 Shares Issued under the universal shelf registration Common Stock [Member]
Class of Stock [Line Items]
Maximum Amount of Offering from Universal Shelf Registration Statement							$ 500,000,000					$ 60,000,000
Shares issued (in shares)																		32,035,064		2,100,000
Common stock, shares authorized		240,000,000	240,000,000		750,000,000	240,000,000								1,882,248
Common stock, issued		184,893,886	184,893,886			179,167,112		32,035,064			2,070,000	553,300					140,700,000
Proceeds from issuances of common stock			$ 490,584,000	$ 825,246,000					$ 490,600,000	$ 26,700,000		$ 8,900,000	$ 455,000,000
Shares, Outstanding															29,200,000	27,700,000	148,113,788.5	184,893,886	179,167,112
Convertible stock issued during period, value															$ 12.00
Dividends declared, in dollars per share	$ 0.94	$ 0.910