Schedule II - Valuation and Qualifying Accounts - Summary of Allowance for Doubtful Accounts and Estimated Liability for Appeals (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
Balance at Beginning of Year	$ 14,799	$ 10,772	$ 11,464
Provision	20,453	20,233	21,583
Recoveries			108
Charge-offs	(21,569)	(16,206)	(22,383)
Balance at End of Year	13,683	14,799	10,772
Estimated Liability for Appeals and Estimated Allowance for Appeals [Member]
Balance at Beginning of Year	8,544	11,126	12,801
Provision		83	721
Recoveries	(108)	(2,665)	(2,396)
Charge-offs	(8,436)
Balance at End of Year		$ 8,544	$ 11,126