Leases - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) Property State	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Property State	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Leases [Line Items]
Number of properties in portfolio | Property	932		932
Number of states in which our properties are located | State	30		30
Revenues from rental properties	$ 29,022,000	$ 24,365,000	$ 57,307,000	$ 48,261,000
Rental income contractually due from tenants in revenues from rental properties included in continuing operations	28,424,000	23,839,000	55,927,000	47,316,000
Revenue recognition adjustments included in revenues from rental properties in continuing operations	598,000	526,000	1,380,000	945,000
Deferred rent receivables reserves	0	0	0	0
Real Estate Taxes and other municipal charges paid then reimbursed by tenants included in revenues and expenses	4,461,000	3,924,000	7,529,000	6,917,000
Lease origination costs	228,000	$ 30,000	228,000	$ 30,000
Net investment in direct financing leases	88,138,000		88,138,000		$ 89,587,000
Net Investments in direct financing lease, minimum lease payments receivable	148,029,000		148,029,000		154,441,000
Net Investment in direct financing lease, unguaranteed estimated residual value	13,979,000		13,979,000		13,979,000
Net Investment in direct financing lease, deferred income	$ 73,870,000		$ 73,870,000		$ 78,833,000
Third Party Landlords [Member]
Leases [Line Items]
Number of properties leased | Property	78		78
Owned Properties [Member]
Leases [Line Items]
Number of properties | Property	854		854