Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Additions for tax positions related to current year	$ 30	$ 518
Effective income tax rate	7.44%
Income tax expense	$ 2,126	869
Income Tax Expense (Benefit), before discrete items	$ (2,096)
Effective Income Tax Rate Reconciliation, Excluding Discrete Items, Percent	7.30%
Unrecognized Tax Benefits	$ 9,173
Unrecognized tax benefits, period increase (decrease)	$ (30)	$ (518)
United States
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Effective income tax rate			7.35%