Collaboration Agreement - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 06, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	$ 9,337,304	$ 8,474,557
Takeda Pharmaceutical Company Limited [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of outstanding capital stock on the issuance date			8.00%
Value fixed on collaboration for share obligation terms			$ 50,000,000
Threshold percentage of outstanding capital stock to make cash payment			19.99%
Global commercial and regulatory milestone payments			$ 35,000,000
Takeda Pharmaceutical Company Limited [Member] | Collaborative Arrangement, Co-promotion [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense reimbursement received	$ 1,257,649
Research and development		$ 432,707