Commitments and Contingencies - Narrative (Details) $ in Thousands	1 Months Ended	2 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Oct. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Oct. 31, 2018 USD ($) ft²
Operating Leased Assets [Line Items]
Office and laboratory space available for rent (in sq ft) | ft²						37,307
Additional renewal term						5 years
Incentive from Lessor						$ 3,100
Rent expense			$ 1,600	$ 1,800	$ 1,900
Amended Lease Agreement [Member] | Building [Member]
Operating Leased Assets [Line Items]
Additional renewal term			5 years
Accrued Lease Obligations [Member]
Operating Leased Assets [Line Items]
Loss on lease		$ 600
Accrued operating lease obligation			$ 500
Accrued operating lease obligation, noncurrent			$ 100
Expected [Member]
Operating Leased Assets [Line Items]
Operating Lease, Payments	$ 15,300