Subsequent Event - Additional Information (Detail) - Alexion Pharmaceuticals Incorporation and Beagle Merger Sub Incorporation - Subsequent Event	Oct. 15, 2019 USD ($) $ / shares shares
Subsequent Event [Line Items]
Right to receive cash under terms of merger agreement | $ / shares	$ 6.30
Merger agreement conversion term	Under the terms of the Merger Agreement, at the time the Merger becomes effective (the “Effective Time”) each share of Company common stock issued and outstanding immediately prior to the Effective Time (other than certain excluded shares as described in the Merger Agreement) will be automatically converted into (i) the right to receive $6.30 in cash, without interest, and (ii) one (1) contractual contingent value right (a “CVR”) pursuant to the CVR agreement that Alexion and a rights agent mutually agreeable to Alexion and the Company will enter into at or prior to the Effective Time.
Agreement termination fee	$ 20,000,000
Merger Agreement Terminated Prior to April 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	30,000,000
Merger Agreement Terminated After April 15, 2020 or Prior to July 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	40,000,000
Merger Agreement Terminated After July 15, 2020 or Prior to October 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	50,000,000
Merger Agreement Terminated After October 15, 2020
Subsequent Event [Line Items]
Agreement termination fee income	$ 60,000,000
In the Money Option
Subsequent Event [Line Items]
Number of CVR called by each share of common stock | shares	1
Out of the Money Option
Subsequent Event [Line Items]
Minimum exercise price payable per share of common stock | $ / shares	$ 8.30