14ner Sales Transaction - Additional Information (Detail) - 14ner Sale [Member]	Jul. 12, 2019 USD ($)
Business Acquisition [Line Items]
Upfront cash payment received	$ 3,500,000
Maximum [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	54,500,000
Maximum [Member] | Achievement of the Primary Endpoint in the First Registrational Clinical Study of Either MM-121 or MM-111 [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	3,000,000
Maximum [Member] | Achievement of Various Regulatory Approval and Reimbursement-Based Milestones in the United States, Europe and Japan [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	16,500,000
Maximum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	35,000,000
Cumulative worldwide net sales target	300,000,000
Minimum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]
Business Acquisition [Line Items]
Cumulative worldwide net sales target	$ 100,000,000