Investments in Real Estate (Details) (USD $)	9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Dec. 31, 2010
Real Estate Properties [Line Items]
Investment in new properties	$ 826,400,000
Purchase price allocation [Abstract]
Net premiums recorded upon assumption of mortgages	957,000
Intangible value of above-market leases	150,124,000				26,221,000
Intangible value of below-market leases	6,600,000				3,452,000
Pro forma Information [Abstract]
Total revenue	342,100,000	[1]	300,400,000	[1]
Income from continuing operations	115,400,000	[1]	92,300,000	[1]
Announced Real Estate Purchase Agreements [Member]
Real Estate Properties [Line Items]
Number of new properties	33
Announced definitive purchase agreements	544,000,000
Announced definitive purchase agreement amount included in current period real estate investments	524,800,000
Announced definitive purchase agreement locations included in current period real estate investments	32
Purchase price allocation [Abstract]
Amount of acquisitions allocated to land	173,400,000
Amount of acquisitions allocated to buildings and improvements	528,300,000
Amount of mortgages payable assumed	67,400,000
Amount of acquisitions allocated to intangible assets	129,900,000
Amount of acquisitions allocated to intangible liabilities	5,200,000
Net premiums recorded upon assumption of mortgages	957,000
Revenues included in consolidated income statement for aggregate acquisitions	15,500,000
Income from continuing operations included in consolidated income statement for aggregate acquisitions	5,100,000
Announced Real Estate Purchase Agreements [Member] | Wholesale Clubs Industry [Member]
Real Estate Properties [Line Items]
Number of properties acquired under long term, triple net lease agreements	6
Amount paid for properties acquired under long term, triple net lease agreements	156,100,000
Announced Real Estate Purchase Agreements [Member] | Health and Fitness Industry [Member]
Real Estate Properties [Line Items]
Number of properties acquired under long term, triple net lease agreements	9
Amount paid for properties acquired under long term, triple net lease agreements	63,200,000
Announced Real Estate Purchase Agreements [Member] | Restaurants - Quick Service Industry [Member]
Real Estate Properties [Line Items]
Number of properties acquired under long term, triple net lease agreements	60
Amount paid for properties acquired under long term, triple net lease agreements	41,900,000
Announced Real Estate Purchase Agreements [Member] | Remaining Properties [Member]
Real Estate Properties [Line Items]
Number of additional properties acquired	18
Amount paid for additional properties acquired	40,400,000
Real Estate Investments [Member]
Real Estate Properties [Line Items]
Investment in new properties	826,400,000		302,900,000
Number of new properties	125		23
Weighted average contractual lease rate (in hundredths)	7.90%		7.60%
Different U.S. state of location	25		8
Leasable square feet (in square feet)	5,500,000		511,000
Leased percentage (in hundredths)	100.00%		100.00%
Average lease term (in years)	11.3Y		18.3Y
Acquisition transaction costs	1,100,000		191,000
Purchase price allocation [Abstract]
Capitalized costs on existing properties	3,000,000		2,300,000
Re-leasing costs included in capitalized costs on existing properties	1,300,000		874,000
Building and tenant improvements included in capitalized costs on existing properties	1,700,000		1,400,000
Real Estate Investments With Existing Leases [Member]
Real Estate Properties [Line Items]
Investment in new properties	573,100,000
Number of new properties	93
Purchase price allocation [Abstract]
Intangible value of the in-place leases	107,600,000
Intangible value of above-market leases	22,300,000
Intangible value of below-market leases	$ 3,500,000

[1] This unaudited pro forma supplemental information does not purport to be indicative of what our operating results would have been had the acquisitions occurred on January 1, 2010, and may not be indicative of future operating results. No material, non-recurring pro-forma adjustments were included in the calculation of this information.