Investments in Real Estate (Details) (USD $)	12 Months Ended										12 Months Ended										12 Months Ended
	Dec. 31, 2012 sqft	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 2.0% notes, issued in October 2012 and due in January 2018	Oct. 31, 2012 2.0% notes, issued in October 2012 and due in January 2018	Jan. 02, 2011 2.0% notes, issued in October 2012 and due in January 2018 Pro Forma	Dec. 31, 2012 3.25% notes, due in October 2022	Oct. 31, 2012 3.25% notes, due in October 2022	Jan. 02, 2011 3.25% notes, due in October 2022 Pro Forma	Dec. 31, 2012 ARCT	Dec. 31, 2012 Crest property	Dec. 31, 2011 Crest property	Dec. 31, 2012 Maximum	Dec. 31, 2012 Restaurant - casual industry Crest property	Dec. 31, 2012 Transportation services	Dec. 31, 2011 Transportation services	Dec. 31, 2012 Drug stores	Dec. 31, 2011 Drug stores	Dec. 31, 2012 Restaurant - quick service	Dec. 31, 2011 Restaurant - quick service	Dec. 31, 2012 New properties and properties under development industry property state sqft	Dec. 31, 2011 New properties and properties under development state industry property sqft	Dec. 31, 2012 Aggregate acquisitions property	Dec. 31, 2011 Aggregate acquisitions property	Dec. 31, 2012 Real estate investments with existing leases property	Dec. 31, 2011 Real estate investments with existing leases property	Dec. 31, 2010 Real estate investments with existing leases
Investments in real estate properties
Investments in real estate	$ 1,160,000,000													$ 890,000							$ 1,160,000,000	$ 1,020,000,000			$ 552,500,000	$ 592,100,000
Number of properties acquired											4	3		1							423	164			129	94
Initial weighted average contractual lease rate of properties acquired (as a percent)																					7.20%	7.80%
Number of states in which properties are located																					37	26
Leasable square feet	37,600,000																				10,500,000	6,200,000
Leased area (as a percent)																					100.00%	100.00%
Average lease term																					14 years 7 months 6 days	13 years 4 months 24 days
Number of industries in which tenants operate																					23	16
Investments to any one tenant as a percentage of total assets													10.00%
Acquisition transaction costs																					2,400,000	1,500,000
Land recorded related to acquisition																							284,500,000	239,300,000
Buildings and improvements recorded																							770,000,000	645,000,000
Intangible assets recorded																							107,200,000	137,000,000
Other assets recorded																							34,900,000
Intangible and assumed liabilities recorded																							32,500,000	5,100,000
Premiums recorded upon assumption of mortgages																							10,000,000	820,000
Number of properties acquired with assumed mortgages payable																							8	4
Number of properties acquired with notes receivable																								1
Assumed mortgages payable	175,868,000	67,781,000																					110,500,000	67,400,000
Total revenue	475,510,000	410,252,000	333,437,000																				23,900,000
Income from continuing operations	145,971,000	144,625,000	115,201,000																				9,800,000
Amount of investment allocated by estimate	106,400,000
Assumed note receivable																								8,800,000
Total capitalized costs on existing properties	7,910,878																						6,600,000	4,200,000
Re-leasing costs included in capitalized costs on existing properties																							1,620,000	1,700,000
Building and tenant improvements included in capitalized costs on existing properties	(6,554,000)	(4,172,000)	(3,578,000)																				4,930,000	2,500,000
Notes payable	2,550,000,000	1,750,000,000		350,000,000		350,000,000	450,000,000		350,000,000
Interest rate (as a percent)				2.00%	2.00%	2.00%	3.25%	3.25%	5.75%
Estimated merger-related transaction costs										19,000,000
Unaudited Pro Forma Information
Total revenue	717,900,000	669,300,000
Income from continuing operations	188,200,000	156,400,000
Intangible value of the in-place leases acquired																									98,600,000	109,900,000
Intangible value of above-market leases acquired																									8,500,000	27,100,000
Intangible value of below-market leases acquired																									21,100,000	3,500,000
In-place lease, amortization to expense																									15,600,000	8,300,000	1,400,000
Net increase (decrease) to rental income for capitalized above market and below market leases																									(1,800,000)	(1,100,000)	154,000
Real estate owned	5,042,137,000	4,160,008,000									3,900,000				130,203,000	107,632,000	159,482,000	154,015,000	251,084,000	277,648,000
Real estate held for investment	5,022,918,000	4,157,855,000									3,000,000	3,000,000
Notes receivable held											$ 18,900,000	$ 19,000,000