Accounts Receivable (Accounts Receivable) (Details) - USD ($) $ in Thousands	Sep. 30, 2018		Dec. 31, 2017
Receivables [Abstract]
Trade receivables	$ 390,575		$ 333,954
Allowance for doubtful accounts	(7,668)		(4,771)
Sales returns allowance	0	[1]	(4,127)
Other allowances	(2,600)		(2,164)
Accounts receivable, net	$ 380,307		$ 322,892

[1] Effective January 1, 2018, as part of the Company’s adoption of Topic 606, the Company has recorded a liability for estimated returns of inventory as a refund liability within accrued expenses and other liabilities. These balances were previously presented as an allowance within accounts receivable. See Note 6 for further details.