Nature of the Business - Additional Information (Detail) - USD ($)					1 Months Ended	3 Months Ended						9 Months Ended
	Dec. 31, 2019	Jul. 12, 2019	May 07, 2019	Apr. 03, 2017	May 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 15, 2019	Dec. 31, 2018	Apr. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Proceeds from sale of equity securities												$ 51,500,000	$ 42,200,000
Proceeds from sale of research and development operations												2,025,000
Special cash dividend paid		$ 20,000,000										$ 20,000,000
Dividend payable date		Sep. 05, 2019										Sep. 05, 2019
Dividend payable, date of record		Aug. 28, 2019										Aug. 28, 2019
Accumulated deficit						$ 543,870,000						$ 543,870,000			$ 523,277,000
Net loss	$ 705,000					705,000	$ 9,430,000	$ 10,458,000	$ (3,989,000)	$ 17,769,000	$ 17,782,000	20,593,000	31,562,000
Cash used in operating activities												28,728,000	46,696,000
Cash and cash equivalents						$ 20,858,000			$ 49,794,000			$ 20,858,000	$ 49,794,000		$ 20,079,000
Silver Creek Pharmaceuticals, Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Proceeds from sale of equity securities			$ 7,800,000		$ 7,800,000
Silver Creek Pharmaceuticals, Inc. [Member] | Laboratory Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Proceeds from sale of research and development operations					$ 1,400,000
Loan Agreement [Member] | Hercules Capital, Inc [Member] | Term Loan [Member]
Summary Of Significant Accounting Policies [Line Items]
Payoff amount														$ 16,000,000
Ipsen [Member] | Ongoing Multi Part Clinical [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable				$ 5,000,000
Ipsen [Member] | First Line Treatment of Metastatic Adenocarcinoma of Pancreas [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable				225,000,000
Ipsen [Member] | After Failure of First Line Chemotherapy [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable				150,000,000
Ipsen [Member] | Additional Indication [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable				75,000,000
Ipsen [Member] | Asset Sale Agreement [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable																$ 455,000,000
Additional payments receivable on achievement of certain milestone events				450,000,000
Servier [Member] | Asset Sale Agreement [Member] | Development and Commercialization Milestones [Member]
Summary Of Significant Accounting Policies [Line Items]
Remaining milestone payments received				5,000,000
Milestone payment received				28,000,000
Maximum amount of milestone payments that can be received				$ 33,000,000
14ner Sale [Member]
Summary Of Significant Accounting Policies [Line Items]
Upfront cash payment received		$ 3,500,000
14ner Sale [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events		54,500,000
14ner Sale [Member] | Maximum [Member] | Achievement of the Primary Endpoint in the First Registrational Clinical Study of Either MM-121 or MM-111 [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events		3,000,000
14ner Sale [Member] | Maximum [Member] | Achievement of Various Regulatory Approval and Reimbursement-Based Milestones in the United States, Europe and Japan [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events		16,500,000
14ner Sale [Member] | Maximum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events		35,000,000
Cumulative worldwide net sales target		300,000,000
14ner Sale [Member] | Minimum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative worldwide net sales target		$ 100,000,000