Commitments and Contingencies - Narrative (Details) $ in Thousands				12 Months Ended
	Mar. 05, 2018 USD ($)	Dec. 22, 2017 USD ($)	Sep. 08, 2016 USD ($)	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Other Commitments [Line Items]
Security deposit | $				$ 1,482
Rental expense paid | $				$ 3,237	$ 2,054	$ 1,630
Corporate office and laboratory space [Member] | San Diego, California [Member]
Other Commitments [Line Items]
Leased office space				43,000
Additional, leased office space				76,700
Corporate office and laboratory space [Member] | Suzhou, China [Member]
Other Commitments [Line Items]
Leased office space				25,381
Laboratory and office space [Member] | San Diego, California [Member]
Other Commitments [Line Items]
Leased office space				6,350
Office space [Member] | San Diego, California [Member]
Other Commitments [Line Items]
Leased office space				1,405
Office space [Member] | Pennsylvania [Member]
Other Commitments [Line Items]
Additional, leased office space				2,734
Office space [Member] | California [Member]
Other Commitments [Line Items]
Additional, leased office space				1,405
Office, laboratory and storage space [Member] | Scotland [Member]
Other Commitments [Line Items]
Leased office space				2,312
Offices, facilities for cGMP fill and finish and storage space [Member] | San Diego, California [Member]
Other Commitments [Line Items]
Additional, leased office space				36,400
Yuhan Agreement Claim [Member] | Pending Litigation [Member]
Other Commitments [Line Items]
Loss contingency, amount of attorneys' fees and expenses sought | $		$ 5,000
Yuhan Agreement Claim [Member] | Pending Litigation [Member] | Subsequent event [Member]
Other Commitments [Line Items]
Company counter offer attorney's fees to be awarded amount | $	$ 850
Yuhan Agreement Claim [Member]
Other Commitments [Line Items]
Aggregate purchase price of common stock warrants | $			$ 10,000