Net Loss per Share Attributable to Athenex, Inc. Common Stockholders - Schedule Outstanding Shares of Common Stock Equivalents Excluded from the Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares	11,452,475	11,219,839
Stock Options and Other Common Stock Equivalents
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares	11,347,475	11,219,839
Unvested Restricted Common Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potential dilutive shares	105,000