Schedule III - Real Estate Assets and Accumulated Depreciation Summary of Transactions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
SEC Schedule III, Real Estate Assets and Accumulated Depreciation [Line Items]
Investment in Real Estate, balance at beginning of period	$ 3,636,935		$ 3,542,023	$ 3,071,094
Additions through capital expenditures	38,181		54,678	433,481
Acquisitions	37,827		36,199	131,348
Asset Impairments	(879)
Reclassifications and other	(6,216)		4,035	(93,900)
Investment in Real Estate, balance at end of period	3,705,848	[1]	3,636,935	3,542,023
Accumulated Depreciation, balance at beginning of period	(960,354)		(834,558)	(815,980)
Depreciation	(105,392)		(125,913)	(113,611)
Disposals/Other	6,162		117	95,033
Asset Impairments	578
Accumulated Depreciation, balance at end of period	$ (1,059,006)	[2]	$ (960,354)	$ (834,558)

[1] The aggregate cost of properties for federal income tax purposes is approximately $3.6 billion at December 31, 2017.

[2] Depreciation is calculated using estimated useful lives of depreciable assets up to 50 years for prison facilities.