Nature of the Business - Additional Information (Detail) - USD ($)						1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Mar. 27, 2020	Dec. 03, 2019	Jul. 25, 2019	Jul. 12, 2019	May 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jul. 31, 2019	Apr. 15, 2019	Apr. 30, 2017	Apr. 03, 2017
Summary Of Significant Accounting Policies [Line Items]
Proceeds from maturities and sales of marketable securities										$ 51,500,000
Proceeds on sale of property and equipment										2,025,000
Special cash dividend paid			$ 6,700,000	$ 20,000,000.0					$ 20,000,000.0
Dividend payable date			Dec. 23, 2019	Sep. 05, 2019					Sep. 05, 2019
Dividend payable, date of record			Dec. 16, 2019	Aug. 28, 2019					Aug. 28, 2019
Accumulated deficit	$ 542,529,000						$ 542,529,000		$ 542,529,000		$ 540,609,000
Net loss							1,006,000	$ 705,000	1,920,000	20,593,000
Cash used in operating activities									2,849,000	$ 28,728,000
Cash, cash equivalents and marketable securities	15,800,000						$ 15,800,000		$ 15,800,000
Silver Creek Pharmaceuticals, Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Proceeds from maturities and sales of marketable securities						$ 7,800,000
Silver Creek Pharmaceuticals, Inc. [Member] | Laboratory Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Proceeds on sale of property and equipment						$ 1,400,000
Celator Pharmaceuticals Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash payment received		$ 2,300,000
Reimbursement of expenses		$ 200,000
Transaction expenses	$ 400,000
Loan Agreement [Member] | Hercules Capital Inc [Member] | Term Loan [Member]
Summary Of Significant Accounting Policies [Line Items]
Payoff Amount													$ 16,000,000.0
IpsenSAMember | First Line Treatment of Metastatic Adenocarcinoma of Pancreas [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable															$ 225,000,000.0
IpsenSAMember | After Failure of First Line Chemotherapy [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable															150,000,000.0
IpsenSAMember | Additional Indication [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable															75,000,000.0
IpsenSAMember | Ongoing Multi Part Clinical
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable											$ 5,000,000.0
IpsenSAMember | Asset Sale Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events															$ 450,000,000.0
IpsenSAMember | Asset Sale Agreement [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable														$ 450,000,000.0
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					3,000,000.0
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					35,000,000.0
Cumulative worldwide net sales target					300,000,000.0
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					$ 100,000,000.0
14ner Sale [Member] | Asset Sale Agreement [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable												$ 54,500,000