Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Accrued interest expense	$ 30	$ 48	$ 53	$ 103
Gross liability for unrecognized tax benefits	2,600		2,600
Unrecognized tax benefits that would impact our effective tax rate	2,100		2,100
Interest included in total liability	400		400
Significant increases or decreases for uncertain tax positions	$ 0		$ 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%