Income Taxes, Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Balance at beginning of year	$ 1,164	$ 957
Additions based on tax positions related to current year	464	0
Additions based on tax positions related to prior years	1,151	207
Reductions for tax positions of prior years	(99)	0
Balance at end of year	$ 2,680	$ 1,164