Notes Payable - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) PromissoryNote	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Carrying value of notes payable	$ 50,061,000	$ 50,061,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Debt Instrument [Line Items]
Debt instrument repayment terms, description		If the approval of andexanet alfa in the USA and EU is not achieved by January 1, 2019, we are able to reduce the repayment amount to $60.0 million if such amount is paid by December 31, 2021 and regardless of the timing of regulatory approval, we may reduce the repayment amount to $62.5 million if such amount is paid by December 31, 2023. Any unpaid amounts shall become immediately due upon: 1) our change of control; 2) event of default; and 3) termination for breach. We have the right to prepay the repayment amount at any time without any penalty.
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Paid by December 31, 2021
Debt Instrument [Line Items]
Repayment amount	$ 60,000,000	$ 60,000,000
Repayment date	Dec. 31, 2021
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Paid by December 31, 2023
Debt Instrument [Line Items]
Repayment amount	$ 62,500,000	62,500,000
Repayment date	Dec. 31, 2023
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Andexanet Alfa License Agreement with All Countries Excluding Japan
Debt Instrument [Line Items]
Percentage of license fees and milestone payments converted to notes payable upon initial regulatory approval not achieved	50.00%
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Japan License Agreement
Debt Instrument [Line Items]
Percentage of payment receivable upon initial regulatory approval not achieved	100.00%
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | USA and EU
Debt Instrument [Line Items]
Initial regulatory approval date	Jan. 01, 2019
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | USA and EU | Andexanet Alfa License Agreement with All Countries Excluding Japan
Debt Instrument [Line Items]
Percentage of net sales to be paid in each quarter	5.00%
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Promissory Notes
Debt Instrument [Line Items]
Proceeds from notes payable	$ 50,000,000
Number of debt instruments | PromissoryNote	2
Promissory notes, face amount	$ 65,000,000	65,000,000
Promissory notes due date	2024-12
Notes payable, accrued interest	$ 60,000	60,000
Carrying value of notes payable	49,800,000	49,800,000
Embedded derivative liabilities	246,000	246,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Promissory Notes | Fair Value, Inputs, Level 3
Debt Instrument [Line Items]
Estimated fair value of notes payable	$ 54,900,000	$ 54,900,000