Divestitures (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Centers	Dec. 31, 2015 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Business	$ 0	$ 19,160	$ 0
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Urgent Care Centers Operated | Centers		17
Sale Price from Divestiture of Businesses		$ 41,492
Gain (Loss) on Disposition of Business		$ 19,160