Subsequent Events (Details)		1 Months Ended	12 Months Ended
	Jan. 26, 2018 USD ($) $ / shares shares	Jan. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Jan. 16, 2018 USD ($) ft²
Subsequent Event [Line Items]
Share price (in dollars per share) | $ / shares			$ 33.89
Proceeds from public offerings, net of offering costs			$ 0	$ 61,822,000	$ 9,657,000
Common Stock
Subsequent Event [Line Items]
Common stock shares sold (in shares) | shares		2,875,000		2,875,000
Share price (in dollars per share) | $ / shares		$ 23.00
Proceeds from public offerings, net of offering costs		$ 61,800,000
Stock options | Over-Allotment Option | Common Stock
Subsequent Event [Line Items]
Common stock shares sold (in shares) | shares		375,000
Subsequent Event | Common Stock
Subsequent Event [Line Items]
Common stock shares sold (in shares) | shares	3,450,000
Share price (in dollars per share) | $ / shares	$ 41.50
Proceeds from public offerings, net of offering costs	$ 134,100,000
Subsequent Event | Stock options | Over-Allotment Option | Common Stock
Subsequent Event [Line Items]
Common stock shares sold (in shares) | shares	450,000
Subsequent Event | Emeryville, LLC
Subsequent Event [Line Items]
Lessee, operating lease, rentable square feet (in sqft) | ft²						37,626
Lessee, operating lease, monthly payments due in first twelve months of lease						$ 159,911
Lessee, operating lease, monthly rent expense increase						$ 5,000