SCHEDULE II. VALUATION AND QUALIFYING ACCOUNTS - Transactions in the Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of year	$ 42,409	$ 39,543	$ 43,455
Provision	15,634	13,489	5,136
Write-offs	(16,912)	(10,623)	(9,048)
Balance, end of year	$ 41,131	$ 42,409	$ 39,543