Significant Accounting Policies - Additional Information (Details)		12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2019 USD ($) segment $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | segment		1
Impairment losses of long lived assets		$ 0	$ 0	$ 0
Recognized impairments on investments		0	0	0
Interest income		3,000,000.0	3,400,000	1,800,000
Operating lease right-of-use assets		16,523,000
Total lease liabilities		17,604,000
Income tax effect		(90,000)	3,000	(1,758,000)
Research and development		$ 91,378,000	$ 86,123,000	$ 72,078,000
Warrants exercise price (in dollars per share) | $ / shares		$ 0.05
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets					$ 17,300,000
Total lease liabilities					$ 17,900,000
Long-term Receivable | Accounting Standards Update 2016-16, Income Tax Effect Deferred From Past Intercompany Transactions
Significant Accounting Policies [Line Items]
Income tax effect	$ 2,100,000