Long-Term Debt - Revolving Lines Of Credit (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Letter of Credit
Line of Credit Facility [Line Items]
Outstanding letters of credit	$ 14,383
Revolver
Line of Credit Facility [Line Items]
Line of credit outstanding amount	300,000	$ 0
Revolving credit facilities	1,000,000
Kidney Care
Line of Credit Facility [Line Items]
Outstanding letters of credit	90,085
DMG
Line of Credit Facility [Line Items]
Outstanding letters of credit	$ 211