Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Operating loss carryforwards, net		$ 4.1
Increase in valuation allowance		10.6	$ 3.9	$ 18.6
State and Local Jurisdiction
Income Taxes [Line Items]
Operating loss carryforwards, net		366.9
Research and development tax credit carryforwards		$ 4.2
State and Local Jurisdiction | Minimum
Income Taxes [Line Items]
Operating loss carryforwards, expiration year		2030
Research and development tax credit, expiration year		2019
State and Local Jurisdiction | Maximum
Income Taxes [Line Items]
Operating loss carryforwards, expiration year		2036
Research and development tax credit, expiration year		2031
Internal Revenue Service (IRS)
Income Taxes [Line Items]
Operating loss carryforwards, net		$ 476.2
Research and development tax credit carryforwards		$ 10.3
Internal Revenue Service (IRS) | Minimum
Income Taxes [Line Items]
Operating loss carryforwards, expiration year		2024
Research and development tax credit, expiration year		2023
Internal Revenue Service (IRS) | Maximum
Income Taxes [Line Items]
Operating loss carryforwards, expiration year		2036
Research and development tax credit, expiration year		2036
United Kingdom
Income Taxes [Line Items]
Operating loss carryforwards, net		$ 6.7
CANbridge | Licensing Agreements
Income Taxes [Line Items]
Upfront payment, withholding taxes		0.1
Collaborations and license agreements, expected milestone receivable	$ 1.0	$ 1.0