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 sales returns and allowances
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 6,319	$ 5,572	$ 5,659
Charged to Costs and Expenses	4,920	2,009	1,262
Charged to Other Accounts	1,518	0	0
Deductions	(3,875)	(1,262)	(1,349)
Balance at End of Period	8,882	6,319	5,572
Deferred tax assets valuation allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	3,604	4,887	6,772
Charged to Costs and Expenses	740	(1,228)	80
Charged to Other Accounts	3,617	0	0
Deductions	0	(55)	(1,965)
Balance at End of Period	$ 7,961	$ 3,604	$ 4,887