Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Shares Available for Grant, Balance	19,034
Options Outstanding, Shares Available for Grant, Granted (unaudited)	(28,000)
Options Outstanding, Shares Available for Grant, Canceled (unaudited)	44,557
Options Outstanding, Shares Available for Grant, Balance	35,591		19,034
Options Outstanding, Shares Subject to Options Outstanding, Balance	420,956
Options Outstanding, Shares Subject to Options Outstanding, Granted (unaudited)	28,000	0
Options Outstanding, Shares Subject to Options Outstanding, Exercised (unaudited)	(700)
Options Outstanding, Shares Subject to Options Outstanding, Canceled (unaudited)	(44,557)
Options Outstanding, Shares Subject to Options Outstanding, Balance	403,699		420,956
Options Outstanding, Shares Subject to Options Outstanding, Exercisable (unaudited)	354,139
Options Outstanding, Weighted-Average Exercise Price, Balance	$ 9.20
Options Outstanding, Weighted-Average Exercise Price, Granted (unaudited)	13.60
Options Outstanding, Weighted-Average Exercise Price, Exercised (unaudited)	7.10
Options Outstanding, Weighted-Average Exercise Price, Canceled (unaudited)	7.10
Options Outstanding, Weighted-Average Exercise Price, Balance	$ 9.71		$ 9.20
Options Outstanding Weighted-Average Remaining Contractual Life (Years), Balance	7 years		7 years 4 months 24 days
Options Outstanding, Aggregate Intrinsic Value, Balance	$ 5,021
Options Outstanding, Aggregate Intrinsic Value, Balance	$ 4,598		$ 5,021