Income Taxes - Reconciliation of Statutory Federal Tax Rates and Effective Tax Rates (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory federal tax (benefit) rate	$ (17,107)	$ (2,736)	$ (4,526)
State taxes	(749)	(67)	609
Foreign dividends and unremitted earnings	(638)	(1,745)	(1,493)
Valuation allowance	(16,363)	1,596	2,456
Taxes on foreign income that differ from U.S. tax rate	(1,361)	(901)	(405)
Executive Compensation limitation	17	1,005	0
Non-deductible stock-based compensation expense	567	135	1,104
Expiration of attributes	1,397	1,478	893
Uncertain tax positions	302	120	435
Other	(146)	59	(317)
Total income tax provision	$ 3,727	$ 2,434	$ 1,742
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal tax (benefit) rate	35.00%	35.00%	35.00%
State taxes	1.50%	0.90%	(4.70%)
Foreign dividends and unremitted earnings	1.30%	(22.30%)	(11.50%)
Valuation allowance	33.50%	(20.40%)	(19.00%)
Taxes on foreign income that differ from U.S. tax rate	2.80%	11.50%	3.10%
Executive Compensation limitation	(0.00%)	(12.90%)	(0.00%)
Non-deductible stock-based compensation expense	(1.20%)	(1.70%)	(8.50%)
Expiration of attributes	(2.90%)	(18.90%)	(6.90%)
Uncertain tax positions	(0.60%)	(1.50%)	(3.40%)
Other	0.40%	(0.80%)	2.40%
Effective tax rate	(7.60%)	(31.10%)	(13.50%)
Impact on tax reform	$ 36,311
Impact on tax reform, percent	(74.30%)
Tax audit settlement	$ 1,497
Tax Audit Settlement, percent	(3.10%)