Income Taxes - Deferred Tax Assets - (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Accruals and reserves	$ 331	$ 331
Deferred rent credit	151	161
Total deferred tax assets	482	492
Deferred tax liabilities:
Depreciation and amortization	(337)	(354)
Total deferred tax liabilities	(337)	(354)
Net deferred tax asset	$ 145	$ 138