Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period		$ 2,000
Balance at End of Period		1,200	$ 2,000
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period		3,889	6,241	$ 3,750
Charged to Expense		3,917	954	5,578
Charged to Other Accounts		9	0	0	[1]
Deductions	[2]	4,395	3,306	3,087
Balance at End of Period		3,420	3,889	6,241
Allowance for returns
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period		1,994	1,438	2,185
Charged to Expense		0	0	0
Charged to Other Accounts	[3]	4,890	2,088	3,276
Deductions	[4]	5,659	1,532	4,023
Balance at End of Period		1,225	1,994	1,438
Valuation allowance for deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period		14,156	16,673	15,167
Charged to Expense		0	0	0
Charged to Other Accounts	[5]	62,633	(2,517)	1,506
Deductions		0	0	0
Balance at End of Period		$ 76,789	$ 14,156	$ 16,673

[1] Adjustments from acquisitions.

[2] Uncollectible accounts written off, net of recoveries.

[3] Charged against revenues.

[4] Credits issued for returns.

[5] Related to deferred tax assets on foreign tax credits, net operating loss carryforwards, and depreciation.