Long Term Obligations - Additional Information (Detail)	1 Months Ended			3 Months Ended
Long Term Obligations - Additional Information (Detail)	Feb. 28, 2019 USD ($)	Feb. 28, 2017 USD ($)	Dec. 31, 2016 USD ($) promissory_note	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	May 31, 2018 USD ($)
Debt Instrument [Line Items]
Gain (loss) on remeasurement of embedded derivatives				$ (3,169,000)	$ 472,000
Andexxa \| HealthCare Royalty Partners and its Affiliates (“HCR”)
Debt Instrument [Line Items]
Accrued interest				$ 48,500,000		$ 44,400,000
Amount received under royalty sales agreement		$ 50,000,000.0
Additional amount receivable upon U.S. regulatory approval		100,000,000.0
Sales agreement fee		2,000,000.0					$ 5,000,000.0
Additional debt issuance costs		$ 600,000
Funding amount							$ 100,000,000.0
Effective interest rate				9.70%
Unamortized debt discount				$ 5,800,000		5,900,000
Ondexxya \| HealthCare Royalty Partners and its Affiliates (“HCR”)
Debt Instrument [Line Items]
Gain (loss) on remeasurement of embedded derivatives				$ (1,600,000)
Remeasurement of embedded derivative to fair value, whole provision lapses from funding date, period				30 months
Ondexxya \| HealthCare Royalty Partners and its Affiliates (“HCR”) \| Secured Term Loan
Debt Instrument [Line Items]
Sales agreement fee				$ 2,800,000
Effective interest rate				11.50%
Debt instrument, maturity date	Feb. 28, 2025
Debt instrument, interest rate	9.75%
Debt instrument, covenant description				The loans are secured by substantially all of our assets. The Credit Agreement contains certain covenants that, among others, require us to deliver financial reports at designated times of the year and limit or restrict our ability to incur additional indebtedness or liens, acquire, own or make any investments, pay cash dividends or enter into certain corporate transactions, including mergers and changes of control, and require us to maintain $50.0 million of cash.
Maintain cash increased	$ 50,000,000.0
Debt instrument default interest rate	12.75%
Other debt issuance cost				$ 500,000
Debt instrument, accrued interest				3,400,000
Debt instrument, interest payment				3,100,000
Ondexxya \| HealthCare Royalty Partners and its Affiliates (“HCR”) \| First Tranche \| Secured Term Loan
Debt Instrument [Line Items]
Promissory notes, face amount	$ 62,500,000
Ondexxya \| HealthCare Royalty Partners and its Affiliates (“HCR”) \| Second Tranche \| Secured Term Loan
Debt Instrument [Line Items]
Promissory notes, face amount	$ 62,500,000
Ondexxya \| Fair Value, Inputs, Level 3 \| HealthCare Royalty Partners and its Affiliates (“HCR”)
Debt Instrument [Line Items]
Estimated fair value of long-term debt				113,700,000		123,700,000
Royalty Based Debt \| Andexxa \| Fair Value, Inputs, Level 3 \| HealthCare Royalty Partners and its Affiliates (“HCR”)
Debt Instrument [Line Items]
Estimated fair value of long-term debt				110,200,000		142,000,000.0
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") \| Promissory Notes
Debt Instrument [Line Items]
Proceeds from notes payable			$ 50,000,000.0
Number of debt instruments \| promissory_note			2
Promissory notes, face amount			$ 65,000,000.0
Promissory notes due date			2024-12
Repayment amount			$ 62,500,000
Repayment date			Dec. 31, 2023
Accrued interest				11,300,000		10,700,000
Gain (loss) on remeasurement of embedded derivatives				(1,600,000)	$ 500,000
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				$ 40,800,000		$ 47,300,000
Scenario Two \| Andexxa \| HealthCare Royalty Partners and its Affiliates (“HCR”) \| Maximum
Debt Instrument [Line Items]
Percentage of royalty obligated to pay of net worldwide sales		8.46%
Scenario Two \| Andexxa \| HealthCare Royalty Partners and its Affiliates (“HCR”) \| Minimum
Debt Instrument [Line Items]
Percentage of royalty obligated to pay of net worldwide sales		4.19%
Scenario Three \| Andexxa \| HealthCare Royalty Partners and its Affiliates (“HCR”)
Debt Instrument [Line Items]
Percentage of royalty obligated to pay of net worldwide sales		195.00%
Scenario Three \| Andexxa \| HealthCare Royalty Partners and its Affiliates (“HCR”) \| Maximum
Debt Instrument [Line Items]
Transaction expense		$ 290,600,000
Scenario Three \| Andexxa \| HealthCare Royalty Partners and its Affiliates (“HCR”) \| Minimum
Debt Instrument [Line Items]
Target payment for royalty obligation		$ 150,000,000.0

PORTOLA PHARMACEUTICALS INC 10-Q