Notes Payable - Additional Information (Detail)	1 Months Ended		3 Months Ended
	Feb. 28, 2017 USD ($)	Dec. 31, 2016 USD ($) PromissoryNote	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Carrying value of Notes			$ 51,370,000		$ 50,565,000
Gain on remeasurement of embedded derivatives			1,634,000
Long-term debt			56,027,000		54,251,000
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa
Debt Instrument [Line Items]
Accrued interest expense			9,200,000		7,400,000
Amount received under royalty sales agreement	$ 50,000,000
Additional amount receivable upon U.S. regulatory approval	$ 100,000,000
Gain on remeasurement of embedded derivatives			$ 2,200,000
Effective interest rate			14.00%
Debt instrument increase, accrued interest			$ 1,800,000	$ 900,000
Royalty sales agreement fee			2,000,000
Additional debt issuance costs			600,000
Interest expense, including amortization of debt discount			1,800,000	$ 900,000
Long-term debt			56,000,000		54,300,000
Outstanding debt, net of unamortized debt discount			2,300,000		2,300,000
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Scenario One
Debt Instrument [Line Items]
Percentage of royalty obligated to pay of net worldwide sales	2.00%
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Scenario Two
Debt Instrument [Line Items]
Target payment for royalty obligation	$ 100,000,000
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Scenario Three
Debt Instrument [Line Items]
Percentage of royalty obligated to pay of net worldwide sales	195.00%
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Fair Value, Inputs, Level 3
Debt Instrument [Line Items]
Estimated fair value of long-term debt			$ 57,800,000		58,800,000
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Maximum
Debt Instrument [Line Items]
Repayment amount	$ 125,000,000
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Maximum | Scenario Two
Debt Instrument [Line Items]
Percentage of royalty obligated to pay of net worldwide sales	7.85%
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Minimum | Scenario Two
Debt Instrument [Line Items]
Percentage of royalty obligated to pay of net worldwide sales	3.58%
HealthCare Royalty Partners and its Affiliates (“HCR”) | Andexxa | Minimum | Scenario Three
Debt Instrument [Line Items]
Target payment for royalty obligation	$ 150,000,000
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
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
Repayment date		Dec. 31, 2023
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Andexxa
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") | United States and EU
Debt Instrument [Line Items]
Initial regulatory approval date		Jan. 01, 2019
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | United States and EU | Andexxa
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") | 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") | 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
Promissory notes due date		2024-12
Accrued interest expense			$ 5,100,000		4,200,000
Carrying value of Notes			51,400,000		50,600,000
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			54,000,000		$ 55,500,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Promissory Notes | Maximum
Debt Instrument [Line Items]
Loss on remeasurement of embedded derivatives			$ 600,000