SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts and revenue reserves
Movement in Valuation Allowances and Reserves
Balance at Beginning of Period	$ 9,177	$ 8,171	$ 6,861
Charges to Earnings	27,514	17,425	13,234
Charges to Other Accounts	271	(56)	(453)
Deductions	(27,699)	(16,363)	(11,471)
Balance at End of Period	9,263	9,177	8,171
Deferred tax valuation allowance
Movement in Valuation Allowances and Reserves
Balance at Beginning of Period	14,180	12,696	11,249
Charges to Earnings	42,310	2,384	2,248
Charges to Other Accounts	5,073	(900)	(801)
Deductions	0	0	0
Balance at End of Period	$ 61,563	$ 14,180	$ 12,696