Stock-Based Compensation - Stock option activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Shares Available for Grant
Beginning of the period (in shares)	144,980
Additional shares reserved (in shares)	77,908	77,908
Options granted (in shares)	(291,100)	(158,918)
Options cancelled (in shares)	68,212	(11,232)
End of the period (in shares)		144,980
Options Outstanding, Number of Shares
Number of Shares, beginning of the period (in shares)	603,291
Number of Shares, Options exercised (in shares)	974
Number of Shares, Options granted (in shares)	291,100	158,918
Number of Shares, Options cancelled (in shares)	(68,212)	(11,232)
Number of Shares, end of the period (in shares)	825,205	603,291
Options Outstanding, Weighted-Average Exercise Price
Weighted-Average Exercise Price, beginning of the period (in dollars per share)	$ 9.52
Weighted-Average Exercise Price, Options exercised (in dollars per share)	9.63
Weighted-Average Exercise Price, Options granted (in dollars per share)	17.21	$ 11.38
Weighted-Average Exercise Price, Options cancelled (in dollars per share)	10.52	4.64
Weighted-Average Exercise Price, end of the period (in dollars per share)	$ 12.15	$ 9.52
Options
Shares Available for Grant
Beginning of the period (in shares)		214,758
Options Outstanding, Number of Shares
Number of Shares, beginning of the period (in shares)		455,605
Number of Shares, Options granted (in shares)	351,516	138,662
Options Outstanding, Weighted-Average Exercise Price
Weighted-Average Exercise Price, beginning of the period (in dollars per share)		$ 8.75