Business Combinations - Narrative (Details) $ in Thousands		1 Months Ended	3 Months Ended	6 Months Ended
	Apr. 05, 2017 USD ($) bed	Jul. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Acquisition of CEC, net of cash acquired				$ 354,466	$ 0
Goodwill			$ 787,803	787,803		$ 615,433
Community Education Centers
Business Acquisition [Line Items]
Number of beds in facility (more than 12,000) | bed	12,000
Percentage of voting interests acquired	100.00%
Acquisition of CEC, net of cash acquired	$ 354,500
Cash acquired from acquisition	3,000
Acquisition related costs	4,100
Debt outstanding	115,000
Goodwill	172,343
Revenue for CEC activity since acquisition			56,700	56,700
Earnings for CEC activity since acquisition			2,600	2,600
Maximum potential adjustment to purchase price	$ 1,900
Acquisition-related Costs | Community Education Centers
Business Acquisition [Line Items]
Acquisition related costs			$ 7,800	$ 10,400
Subsequent Event | Community Education Centers
Business Acquisition [Line Items]
Purchase price adjustment, decrease		$ 2,600