Schedule II Valuation and Qualifying Accounts - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 396	$ 287	$ 489
Additions charged to costs and expenses	20	231	168
Other Additions	0	0	0
Deductions	(366)	(122)	(370)
Balance at end of period	50	396	287
Allowance for sales discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	103	118	181
Additions charged to costs and expenses	811	1,087	1,334
Other Additions	0	0	0
Deductions	(838)	(1,102)	(1,397)
Balance at end of period	76	103	118
Allowance for chargebacks
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	3,663	4,749	3,023
Additions charged to costs and expenses	41,387	41,941	41,991
Other Additions	0	0	0
Deductions	(44,642)	(43,027)	(40,265)
Balance at end of period	408	3,663	4,749
Deferred tax asset valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	52,144	53,184	33,949
Additions charged to costs and expenses	35,500	7,509	19,328
Other Additions	0	5,581	5,544
Deductions	(26,407)	(14,130)	(5,637)
Balance at end of period	$ 61,237	$ 52,144	$ 53,184