Schedule III - Reconciliation of Real Estate and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SEC Schedule III, Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Beginning balance	$ 293,003	$ 618,844	$ 607,133
Amounts capitalized	105,611	89,780	124,633
Amounts retired or adjusted	(87,987)	(415,621)	(112,922)
Ending balance	310,627	293,003	618,844
Beginning balance	0	(32,129)	(31,377)
Depreciation expense	0	(816)	(6,810)
Amounts retired or adjusted	0	32,945	6,058
Ending balance	$ 0	$ 0	$ (32,129)