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	$ 16,405	$ 16,528	$ 12,437
Charges to Earnings	28,930	17,733	16,648
Charges to Other Accounts	(1,006)	(695)	(536)
Deductions	(32,840)	(17,161)	(12,021)
Balance at end of period	11,489	16,405	16,528
Sales returns accrual
Movement in Valuation Allowances and Reserves
Balance at beginning of period	80	828	1,119
Charges to Earnings	0	14,998	17,569
Charges to Other Accounts	(80)	(962)	0
Deductions	0	(14,784)	(17,860)
Balance at end of period	0	80	828
Deferred tax valuation allowance
Movement in Valuation Allowances and Reserves
Balance at beginning of period	88,170	90,482	98,350
Charges to Earnings	38,144	(837)	(6,072)
Charges to Other Accounts	6,284	(1,475)	(1,796)
Deductions	0	0	0
Balance at end of period	132,598	88,170	90,482
Other reserves
Movement in Valuation Allowances and Reserves
Balance at beginning of period	2,822	2,801	2,204
Balance at end of period	$ 2,544	$ 2,822	$ 2,801