Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Accrued interest expense	$ 23	$ 55
Gross liability for unrecognized tax benefits	2,800
Unrecognized tax benefits that would impact our effective tax rate	2,200
Interest included in total liability	400
Significant increases or decreases for uncertain tax positions	$ 0
Federal corporate tax rate				35.00%
State and Foreign Tax Authorities | Minimum
Income Tax Examination [Line Items]
Period of statute of limitations (years)	3 years
State and Foreign Tax Authorities | Maximum
Income Tax Examination [Line Items]
Period of statute of limitations (years)	4 years
Statutory federal income tax rate [Domain]
Income Tax Examination [Line Items]
Federal corporate tax rate			21.00%