Investments in Real Estate (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended			6 Months Ended													3 Months Ended	6 Months Ended
	Jun. 30, 2014 sqft	Jun. 30, 2013	Jun. 30, 2014 item sqft	Jun. 30, 2013	Mar. 31, 2013 ARCT sqft item	Jun. 30, 2013 ARCT	Mar. 31, 2013 ARCT Retail properties	Mar. 31, 2013 ARCT Office properties	Mar. 31, 2013 ARCT Industrial and distribution properties	Jun. 30, 2014 Inland sqft	Jun. 30, 2014 Maximum	Jun. 30, 2014 New properties and properties under development or expansion item sqft	Jun. 30, 2013 New properties and properties under development or expansion item sqft	Jun. 30, 2014 New properties and properties under development or expansion Retail properties	Jun. 30, 2013 New properties and properties under development or expansion Retail properties	Jun. 30, 2014 New properties and properties under development or expansion Office properties	Jun. 30, 2013 New properties and properties under development or expansion Office properties	Jun. 30, 2014 New properties and properties under development or expansion Industrial and distribution properties	Jun. 30, 2013 New properties and properties under development or expansion Industrial and distribution properties	Jun. 30, 2014 New properties and properties under development or expansion Manufacturing properties	Jun. 30, 2013 New properties and properties under development or expansion Manufacturing properties	Jun. 30, 2014 Properties under development or expansion item	Jun. 30, 2014 Aggregate acquisitions	Jun. 30, 2014 Aggregate acquisitions	Jun. 30, 2013 Aggregate acquisitions	Jun. 30, 2014 Investments in Existing Properties	Jun. 30, 2013 Investments in Existing Properties	Jun. 30, 2014 Real estate investments with existing leases item	Jun. 30, 2013 Real estate investments with existing leases item
Investments in real estate properties
Investments in properties																						$ 35,600,000
Real estate acquired and developed					3,200,000,000					502,900,000		1,060,000,000	866,500,000												4,000,000,000			789,800,000	3,970,000,000
Number of properties					515							402	206									21						149	712
Initial weighted average contractual lease rate of properties acquired (as a percent)												7.10%	7.00%									8.50%
Number of states in which properties are located					44							39	35
Leasable square feet	69,100,000		69,100,000		16,000,000							6,900,000	5,100,000
Leased area (as a percent)					100.00%					100.00%		100.00%	100.00%
Weighted average lease term					12 years 2 months 12 days							12 years 9 months 18 days	13 years 9 months 18 days
Number of properties in the portfolio					69					84
Number of industries in which tenants operate					28							24	17
Property type- percentage of properties acquired							54.00%	13.40%	32.60%					83.00%	86.10%	8.50%	5.40%	6.80%	4.70%	1.70%	3.80%
Net Discounts/(Premiums) recorded upon assumption of mortgages																								(718,000)	(28,400,000)
Acquisition transaction costs						12,600,000						645,000	818,000
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																								209,200,000	597,600,000
Buildings and improvements recorded																								721,400,000	2,790,000,000
Intangible assets related to leases recorded																								161,800,000	726,400,000
Other assets recorded																								901,000	13,700,000
Intangible liabilities related to leases and other assumed liabilities recorded																								30,900,000	96,700,000
Mortgages acquired			159,700,000	113,700,000																				159,700,000
Increase in net income from change in valuation of purchase price allocation measurement		1,800,000		3,200,000
Contingent consideration associated with acquisition	0	0	0	0
Total revenue	228,646,000	186,443,000	450,218,000	361,965,000																				24,400,000
Income from continuing operations	62,221,000	51,944,000	117,138,000	85,311,000																				9,400,000
Amount of investment allocated by estimate																							389,700,000
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 quarter of 2014 finalized during the period																								400,100,000
Total capitalized costs on existing properties																										2,700,000	3,300,000
Re-leasing costs included in capitalized costs on existing properties																										467,000	774,000
Building and tenant improvements included in capitalized costs on existing properties																										2,300,000	2,500,000
In-place lease, depreciation and amortization to expense			40,800,000	28,700,000
Net (increase) decrease to rental income for capitalized above market and below market leases			4,200,000	4,200,000
Net decrease to rental revenue
2014	(4,159,000)		(4,159,000)
2015	(8,372,000)		(8,372,000)
2016	(8,384,000)		(8,384,000)
2017	(8,355,000)		(8,355,000)
2018	(8,110,000)		(8,110,000)
Thereafter	(9,141,000)		(9,141,000)
Totals	(46,521,000)		(46,521,000)
Increase to amortization expense
2014	42,409,000		42,409,000
2015	83,323,000		83,323,000
2016	82,951,000		82,951,000
2017	81,726,000		81,726,000
2018	79,280,000		79,280,000
Thereafter	457,160,000		457,160,000
Totals	$ 826,849,000		$ 826,849,000