Investments in Real Estate (Details) (USD $)	3 Months Ended
	Mar. 31, 2013 item sqft	Mar. 31, 2012
Investments in real estate properties
Leasable square feet	53,700,000
Number of investments in properties that caused any tenant to be 10% of more of total assets	0
Contingent consideration associated with acquisition	$ 0
Total revenue	171,695,000	112,305,000
Income from continuing operations	32,333,000	37,047,000
Building and tenant improvements included in capitalized costs on existing properties	(1,678,000)	(1,059,000)
In-place lease, depreciation and amortization to expense	15,000,000	3,300,000
Net (increase) decrease to rental income for capitalized above market and below market leases	565,000	483,000
Net decrease to rental revenue
2013	(2,097,000)
2014	(2,871,000)
2015	(2,815,000)
2016	(2,807,000)
2017	(2,793,000)
Thereafter	(10,584,000)
Totals	(23,967,000)
Increase to amortization expense
2013	53,635,000
2014	71,041,000
2015	70,163,000
2016	69,965,000
2017	69,276,000
Thereafter	387,477,000
Totals	721,557,000
Pro Forma
Increase to amortization expense
Estimated merger-related costs	11,500,000
Pro Forma Information
Total revenue	182,900,000	159,200,000
Income from continuing operations	47,300,000	32,100,000
ARCT
Investments in real estate properties
Investments in properties	3,200,000,000
Number of properties	515
Number of states in which properties are located	44
Leasable square feet	16,000,000
Leased area (as a percent)	100.00%
Weighted average lease term	12 years 2 months 12 days
Number of tenants	69
Number of industries in which tenants operate	28
Acquisition transaction costs	12,000,000
Maximum
Investments in real estate properties
Investments to any one tenant as a percentage of total assets	10.00%
New properties and properties under development or expansion
Investments in real estate properties
Investments in properties	128,400,000	10,700,000
Number of properties	27	11
Initial weighted average contractual lease rate of properties acquired (as a percent)	7.90%	9.00%
Number of states in which properties are located	16	6
Leasable square feet	477,000	34,000
Leased area (as a percent)	100.00%	100.00%
Weighted average lease term	13 years 9 months 18 days	15 years 2 months 12 days
Acquisition transaction costs	143,000	242,000
New properties
Investments in real estate properties
Number of properties	27
Number of industries in which tenants operate	7
Aggregate acquisitions
Investments in real estate properties
Investments in properties	3,300,000,000
Number of properties	529
Land recorded related to acquisition	455,200,000
Buildings and improvements recorded	2,280,000,000
Intangible assets recorded	626,400,000
Other assets recorded	9,400,000
Intangible and assumed liabilities recorded	104,700,000
Premiums recorded upon assumption of mortgages	26,800,000
Total revenue	36,500,000
Income from continuing operations	6,400,000
Amount of investment allocated by estimate	3,200,000,000
Amount of investment previously allocated by estimate finalized during the period	106,400,000
Investments in Existing Properties
Investments in real estate properties
Total capitalized costs on existing properties	1,700,000	1,100,000
Re-leasing costs included in capitalized costs on existing properties	413,000	266,000
Building and tenant improvements included in capitalized costs on existing properties	1,300,000	793,000
Real estate investments with existing leases
Investments in real estate properties
Investments in properties	3,200,000,000
Number of properties	524
Intangible value of the in-place leases acquired	530,000,000
Intangible value of above-market leases acquired	96,400,000
Intangible value of below-market leases acquired	$ 77,900,000