Schedule III - Real Estate and Accumulated Depreciation and Amortization - Schedule of Changes in Real Estate Assets and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment in real estate:
Balance at beginning of year	$ 782,166	$ 783,233	$ 595,959
Acquisitions and capital expenditures	205,598	19,097	233,785
Impairments	(10,623)	(13,590)	(20,606)
Sales and condemnations	(4,520)	(6,379)	(25,019)
Lease expirations/settlements	(1,657)	(195)	(886)
Balance at end of year	970,964	782,166	783,233
Accumulated depreciation and amortization:
Balance at beginning of year	120,576	107,370	100,690
Depreciation and amortization	17,018	16,629	15,663
Impairments	(1,301)	(776)	(3,246)
Sales and condemnations	(1,229)	(2,559)	(5,313)
Lease expirations/settlements	(1,711)	(88)	(424)
Balance at end of year	$ 133,353	$ 120,576	$ 107,370