Deferred Revenue - Summary of Deferred Revenue Activity (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Movement in Deferred Revenue [Roll Forward]
Balance at beginning of period	$ 1,212
Additions to deferred revenue	2,400
Recognized as revenue	(2,238)
Balance at end of period	1,374
BED
Movement in Deferred Revenue [Roll Forward]
Balance at beginning of period	644
Additions to deferred revenue	0
Recognized as revenue	(644)
Balance at end of period	0
Grants
Movement in Deferred Revenue [Roll Forward]
Balance at beginning of period	568
Additions to deferred revenue	2,400
Recognized as revenue	(1,594)
Balance at end of period	$ 1,374