Commitments and Contingencies - Operating Leases (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2017 ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Feb. 29, 2016 USD ($) ft²
Future annual minimum lease payments
Rent expense		$ 1,200	$ 2,500	$ 1,000
Hurley Street Lease
Commitments and contingencies
Leased space ( in square feet) | ft²					59,783
Security deposit					$ 1,600
Estimated useful life			30 years
Extended lease option (in years)		5 years
Future annual minimum lease payments
2018		$ 4,055
2019		4,155
2020		4,257
2021		4,362
2022		4,470
2023 and after		3,801
Total minimum lease payments		25,100
Facility Sublease Arrangement
Commitments and contingencies
Leased space ( in square feet) | ft²	10,000
Future minimum rental revenue to be received		$ 400
Sublease term	18 months
Lease extension term	18 months