Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ (180,934)	$ (172,937)	$ (211,070)	$ (62,304)	$ (353,871)	$ (273,374)
Denominator:
Weighted average common shares outstanding - basic and diluted (shares)	58,742,329		45,226,434		57,577,384	44,736,971
Net loss per share attributable to common shareholders of Biohaven Pharmaceutical Holding Company Ltd - basic and diluted (in dollars per share)	$ (3.08)		$ (4.67)		$ (6.15)	$ (6.11)