Income Taxes Effective Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. Federal tax benefit at statutory rate									$ (1,629)	$ (1,372)
State tax benefit, net of federal benefit									(187)	(171)
U.S.-Foreign rate differential									(113)	(96)
Change in valuation allowance									(33,001)	939
Rate differential impact - Tax Cuts and Jobs Act									34,679	0
Research and development credits									281	233
Permanent items									30	657
Others									(88)	(8)
Total income tax expense	$ (53)	$ 2	$ 29	$ (6)	$ 102	$ 23	$ 51	$ 6	$ (28)	$ 182