Leases - Leasing Activities - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2015 USD ($) Property Portfolios	Jun. 30, 2014 USD ($)
Leases [Line Items]
Number of new triple net leases entered into during the period | Portfolios	15
Number of leased properties with new tenants | Property	440
Properties under license agreements | Property	16
Maximum lease commitment for capital expenditure	$ 12,945,000
Asset retirement obligations removed from balance sheet	13,033,000
Deferred rental revenue	2,478,000
Lease origination costs	90,000	$ 60,000
USTs [Member]
Leases [Line Items]
Asset retirement obligations removed from balance sheet	13,033,000
Net asset cost related to USTs removed from the balance sheet	10,555,000
Deferred rental revenue	$ 2,478,000
Minimum [Member]
Leases [Line Items]
Unitary triple-net lease agreements initial terms	15 years
Maximum [Member]
Leases [Line Items]
Unitary triple-net lease agreements initial terms	20 years
Unitary triple-net lease agreements successive terms	20 years