Subsequent Events (Details)				3 Months Ended
	May 02, 2019 bed contract	Apr. 25, 2019 bed	Apr. 03, 2019 $ / shares	Mar. 31, 2019 $ / shares	Mar. 31, 2018 $ / shares
Subsequent Event [Line Items]
Dividends declared per share (in dollars per share) | $ / shares				$ 0.48	$ 0.47
Subsequent Event
Subsequent Event [Line Items]
Dividends declared per share (in dollars per share) | $ / shares			$ 0.48
Subsequent Event | Bureau Of Prisons (BOP)
Subsequent Event [Line Items]
Contract term	10 years
Subsequent Event | Bureau Of Prisons (BOP) | North Lake Correctional Facility
Subsequent Event [Line Items]
Contract term	10 years
Number of beds in detention facility	1,800
Subsequent Event | Bureau Of Prisons (BOP) | Reeves County Detention Center I & II
Subsequent Event [Line Items]
Contract term	10 years
Number of beds in detention facility	1,800
Number of new contracts | contract	2
Subsequent Event | Bureau Of Prisons (BOP) | Reeves County Detention Center III
Subsequent Event [Line Items]
Number of beds in detention facility	1,376
Subsequent Event | Immigration and Customs Enforcement | South Louisiana ICE Processing Center
Subsequent Event [Line Items]
Number of beds in detention facility		1,000