Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended			6 Months Ended		1 Months Ended	3 Months Ended
	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Dec. 31, 2011	Apr. 19, 2011 STAG Predecessor Group	Apr. 19, 2011 STAG Predecessor Group	Apr. 19, 2011 STAG Predecessor Group
Supplemental cash flow information
Cash paid for interest	$ 2,927,000			$ 7,895,000				$ 2,433,000
Supplemental schedule of noncash investing and financing activities
Acquisition of tangible assets	(204,116,000)		(204,116,000)
Acquisition of goodwill upon formation transactions	(4,923,000)		(4,923,000)
Acquisition of intangible assets upon formation transactions			(83,442,000)
Assumption of mortgage notes payable			190,548,000
Fair market value adjustment to mortgage notes payable acquired	141,000		141,000
Assumption of related party notes payable upon formation transactions	4,466,000
Acquisition of intangible liabilities upon formation transactions	1,066,000		1,066,000
Acquisition of interest rate swaps upon formation transactions included in the purchase price allocation	420,000
Acquisition of other liabilities upon formation transactions			171,000
Issuance of units for acquisition of net assets upon formation transactions	95,670,000
Disposition of accrued lender fees upon formation transactions						4,420,000	4,420,000	4,420,000
Assumption of bridge loan for Option Properties upon formation transactions						(4,750,000)	(4,750,000)	(4,750,000)
Assumption of note payable to related party for Option Properties upon formation transactions						(727,000)	(727,000)	(727,000)
Assumption of interest rate swaps to related party for Option Properties upon formation transactions						(352,000)	(352,000)	(352,000)
Noncash investing activities included in additions of land and building improvements				(303,000)
Dividends and distributions declared but not paid		10,287,000		10,287,000	6,160,000
Accrued distribution upon formation transactions							(1,392,000)
Restricted Cash
Amount held by the company's transfer agent for preferred stock dividends		1,600,000		1,600,000
Tenant Accounts Receivable, net
Allowance for doubtful accounts		700,000		700,000	500,000
Accrued rental revenue		5,200,000		5,200,000	4,500,000
Allowance on accrued rental revenue		200,000		200,000	400,000
Lease security deposits available in existing letters of credit		3,300,000		3,300,000	3,600,000
Lease security deposits available in cash		1,700,000		1,700,000	1,200,000
Deferred Costs
Amortization of deferred financing fees	300,000	300,000		600,000		0		31,000
Revenue Recognition
Estimated amount of real estate taxes, which are the responsibility of tenants	1,000,000	1,600,000		3,000,000		100,000		500,000
Income Taxes
Required minimum percentage distribution of ordinary taxable income to stockholders to qualify as a REIT (as a percent)				90.00%
State and local income, excise and franchise taxes		$ 9,000		$ 100,000