Summary of Significant Accounting Policies, Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Expenses [Abstract]
Accrued sales force commissions and other payments	$ 128,022	$ 151,549
Accrued income taxes	6,674	13,075
Accrued other taxes	38,693	44,580
Accrued payroll and other employee expenses	68,155	38,167
Accrued payable to vendors	34,539	29,874
Accrued royalties	3,899	2,623
Sales return reserve	3,577	4,523
Deferred revenue	20,104	12,669
Other	18,920	22,129
Total accrued expenses	$ 322,583	$ 319,189