Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Additions for tax positions related to current year	$ 55	$ 700	$ 3,335
Effective income tax rate	(0.84%)		0.48%
Income tax expense	$ (204)	$ 789	$ 363	$ 1,121
Income Tax Expense (Benefit), before discrete items	$ 258		$ 532
Effective Income Tax Rate Reconciliation, Excluding Discrete Items, Percent	(1.10%)		0.70%
Unrecognized Tax Benefits	$ 6,600		$ 6,600
Unrecognized tax benefits, period increase (decrease)			$ (3,335)	$ (700)
United States
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Effective income tax rate					0.72%