Subsequent Event - Additional Information (Detail) (Subsequent Event [Member], USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2013 Lease	May 09, 2013 Transactions
Subsequent Event [Line Items]
Sale/leaseback transaction investment		$ 72.5
Sale/leaseback, initial term in years	15 years
Number of sale/leaseback transactions		2
Number of Triple-Net Unitary Leases	2
Number of Lease Renewal Options	3
Amount of 1031 Exchange Proceeds Used To Finance Acquisition	11.5
Amount of Credit Line Borrowings Used to Finance Acquisition	$ 57.5
Mobil Gasoline Station [Member]
Subsequent Event [Line Items]
Acquisition of real estate assets	16
Exxon and Shell Gasoline Station [Member]
Subsequent Event [Line Items]
Acquisition of real estate assets	20