Subsequent Events - (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Jul. 31, 2018 payment $ / shares shares	Aug. 08, 2018 USD ($)	Dec. 31, 2017 payment	May 04, 2017 payment
Subsequent Events | Arizona manufacturing facility
Subsequent events
Total minimum lease payments | $		$ 2.4
2017 Credit Facility
Subsequent events
Number of interest and principal payments			24
End-of-term fee (as a percent)				6.00%
2017 Credit Facility | Minimum
Subsequent events
Number of interest and principal payments				24
2017 Credit Facility | Maximum
Subsequent events
Number of interest and principal payments				36
2017 Credit Facility | Subsequent Events
Subsequent events
End-of-term fee (as a percent)	7.00%
Number of shares the warrant can be converted to | shares	9,375
Warrant exercise price | $ / shares	$ 8.91
Warrant exercise expiration period	5 years
2017 Credit Facility | Subsequent Events | Minimum
Subsequent events
Number of interest and principal payments	24
2017 Credit Facility | Subsequent Events | Maximum
Subsequent events
Number of interest and principal payments	36
SVB Credit Facility | Subsequent Events
Subsequent events
Number of shares the warrant can be converted to that was cancelled | shares	9,229