Schedule II - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves
Balance at beginning of year	$ 14,786	$ 13,999	$ 11,541
Additions charged to expense	9,720	8,081	7,179
Deductions	(6,889)	(7,294)	(4,721)
Balance at end of year	17,617	14,786	13,999
Valuation allowance for deferred tax asset
Movement in Valuation Allowances and Reserves
Balance at beginning of year	178,156	127,095	132,624
Additions charged to expense	3,682	53,782	6,523
Deductions	(39,342)	(2,721)	(12,052)
Balance at end of year	$ 142,496	$ 178,156	$ 127,095