Collaboration Agreements - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended
	Dec. 21, 2017	Aug. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional funding receivable			$ 210,000		$ 8,000,000
Research and development			8,943,000	$ 10,960,000
Collaborative Arrangements [Member] | Phase 2 MRCT [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum contribution amount to clinical trial			3,000,000
Collaborative Arrangements [Member] | Reneo [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License fee received	$ 3,000,000
Unrecognized amount of transaction price allocated to performance obligation			$ 4,500,000
Remainder of performance obligation expected recognition period			14 months 15 days
Collaboration revenue recognized			$ 900,000
Collaborative Arrangements [Member] | Reneo [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential development and regulatory milestone payments	94,500,000
Collaborative Arrangements [Member] | Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License fee received	8,000,000
Potential regulatory milestone payments based on regulatory approval	20,000,000
Potential sales-based milestones based on tiered sales of licensed products	50,000,000
Collaborative Arrangements [Member] | Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. [Member] | Phase 2 MRCT [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum contribution amount to clinical trial	3,000,000
Collaborative Arrangements [Member] | Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. [Member] | Phase 2 MRCT [Member] | License and Technology Transfer Services of Chemistry and Manufacturing Know-How [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Unrecognized amount of transaction price allocated to performance obligation			$ 5,600,000
Remainder of performance obligation expected recognition period			14 months 15 days
Collaboration revenue recognized			$ 1,100,000
Collaborative Arrangements [Member] | Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. [Member] | Obligation to Sponsor and Conduct Portion of Phase 2 MRCT [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue recognized			0
Collaborative Arrangements [Member] | Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. [Member] | Obligation to Participate in Joint Development Committee to Oversee Development of Products and Phase 2 MRCT [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue recognized			0
Collaborative Arrangements [Member] | Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential development and regulatory milestone payments	$ 25,000,000
Collaborative Arrangements [Member] | JDRF [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum research funding receivable achievement based on research and development milestones		$ 3,000,000
Maximum funding percentage of research and development milestones		50.00%
Funding received			300,000
Additional funding receivable			200,000
Research and development			300,000
Changes in estimated transaction prices			$ 0