Investments in Real Estate (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended			9 Months Ended													3 Months Ended	9 Months Ended
	Sep. 30, 2014 sqft	Sep. 30, 2013	Sep. 30, 2014 item sqft	Sep. 30, 2013	Mar. 31, 2013 ARCT sqft item	Sep. 30, 2013 ARCT	Mar. 31, 2013 ARCT Retail properties	Mar. 31, 2013 ARCT Office properties	Mar. 31, 2013 ARCT Industrial and distribution properties	Sep. 30, 2014 Maximum	Sep. 30, 2014 New properties and properties under development or expansion item sqft	Sep. 30, 2013 New properties and properties under development or expansion item sqft	Sep. 30, 2014 New properties and properties under development or expansion Retail properties	Sep. 30, 2013 New properties and properties under development or expansion Retail properties	Sep. 30, 2014 New properties and properties under development or expansion Office properties	Sep. 30, 2013 New properties and properties under development or expansion Office properties	Sep. 30, 2014 New properties and properties under development or expansion Industrial and distribution properties	Sep. 30, 2013 New properties and properties under development or expansion Industrial and distribution properties	Sep. 30, 2014 New properties and properties under development or expansion Manufacturing properties	Sep. 30, 2013 New properties and properties under development or expansion Manufacturing properties	Sep. 30, 2014 Properties under development or expansion item	Sep. 30, 2013 Properties under development or expansion item	Sep. 30, 2014 Aggregate acquisitions	Sep. 30, 2014 Aggregate acquisitions	Sep. 30, 2013 Aggregate acquisitions	Sep. 30, 2014 Investments in Existing Properties	Sep. 30, 2013 Investments in Existing Properties	Sep. 30, 2014 Real estate investments with existing leases item	Sep. 30, 2013 Real estate investments with existing leases item
Investments in real estate properties
Investments in properties																					$ 69,000,000	$ 28,800,000
Real estate acquired and developed					3,200,000,000						1,240,000,000	1,370,000,000													4,500,000,000			949,600,000	4,300,000,000
Number of properties					515						439	407									32	19						180	756
Initial weighted average contractual lease rate of properties acquired (as a percent)											7.10%	7.00%									8.50%	8.50%
Number of states in which properties are located					44						42	40
Leasable square feet	69,800,000		69,800,000		16,000,000						8,500,000	8,000,000
Leased area (as a percent)					100.00%						100.00%	100.00%
Weighted average lease term					12 years 2 months 12 days						12 years 7 months 6 days	14 years 1 month 6 days
Number of properties in the portfolio					69
Number of industries in which tenants operate					28						27	21
Property type- percentage of properties acquired							54.00%	13.40%	32.60%				85.60%	84.10%	7.20%	10.40%	5.80%	3.10%	1.40%	2.40%
Net Discounts/(Premiums) recorded upon assumption of mortgages																								(604,000)	(28,400,000)
Acquisition transaction costs						12,900,000					589,000	1,700,000
Number of investments in properties that caused any tenant to be 10% of more of total assets			0
Investments to any one tenant as a percentage of total assets										10.00%
Land recorded related to acquisition																								240,100,000	769,400,000
Buildings and improvements recorded																								861,900,000	3,100,000,000
Intangible assets related to leases recorded																								202,000,000	765,300,000
Other assets recorded																								901,000	13,500,000
Intangible liabilities related to leases and other assumed liabilities recorded																								60,500,000	115,000,000
Mortgages acquired			166,700,000	81,300,000																				166,700,000
Contingent consideration associated with acquisition	0	0	0	0
Total revenue	235,713,000	202,081,000	685,932,000	564,045,000																				47,300,000
Income from continuing operations	73,627,000	45,508,000	190,766,000	130,819,000																				19,200,000
Amount of investment allocated by estimate																							159,800,000
Amount of investment previously allocated by estimate in the fourth quarter of 2013 finalized during the period																								120,800,000
Amount of investment previously allocated by estimate in the first two quarters of 2014 finalized during the period																								789,800,000
Total capitalized costs on existing properties																										4,500,000	5,900,000
Re-leasing costs included in capitalized costs on existing properties																										655,000	1,100,000
Building and tenant improvements included in capitalized costs on existing properties																										3,900,000	4,800,000
In-place lease, depreciation and amortization to expense			62,100,000	46,400,000
Net (increase) decrease to rental income for capitalized above market and below market leases			6,400,000	6,200,000
Net increase (decrease) to rental revenue
2014	(2,066,000)		(2,066,000)
2015	(8,271,000)		(8,271,000)
2016	(8,283,000)		(8,283,000)
2017	(8,227,000)		(8,227,000)
2018	(7,968,000)		(7,968,000)
Thereafter	14,066,000		14,066,000
Totals	(20,749,000)		(20,749,000)
Increase to amortization expense
2014	21,543,000		21,543,000
2015	84,970,000		84,970,000
2016	84,598,000		84,598,000
2017	83,399,000		83,399,000
2018	80,955,000		80,955,000
Thereafter	481,502,000		481,502,000
Totals	$ 836,967,000		$ 836,967,000