Commitments and Contingencies - Narrative (Details) ft² in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) ft² building	Jun. 30, 2017 USD ($)
Other Commitments [Line Items]
Number of buildings occupied | building			2
Unoccupied lease charges	$ 658	$ 0	$ 658	$ 0
Lease liability, current	300		300
Lease liability, non-current	500		500
Monthly rent expense under operating lease	$ 1,100	$ 1,100	$ 2,200	$ 2,200
Lease One
Other Commitments [Line Items]
Leased square feet | ft²			67
Lease renewal term	5 years		5 years
Lease Two
Other Commitments [Line Items]
Leased square feet | ft²			129
Lease renewal term	10 years		10 years