Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (196,628)	$ (180,934)	$ (172,937)	$ (106,167)	$ (211,070)	$ (62,304)	$ (550,499)	$ (379,541)
Less: Net loss attributable to non-controlling interests	(1,439)			0			(1,439)	0
Net loss attributable to Biohaven Pharmaceutical Holding Company Ltd.	$ (195,189)			$ (106,167)			$ (549,060)	$ (379,541)
Denominator:
Weighted average common shares outstanding - basic and diluted (shares)	59,677,989			52,077,240			58,282,697	47,210,615
Net loss per share attributable to common shareholders of Biohaven Pharmaceutical Holding Company Ltd - basic and diluted (in dollars per share)	$ (3.27)			$ (2.04)			$ (9.42)	$ (8.04)