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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss	$ (106,167)	$ (211,070)	$ (62,304)	$ (61,441)	$ (39,269)	$ (85,462)	$ (379,541)	$ (186,172)
Denominator:
Weighted average common shares outstanding - basic and diluted (shares)	52,077,240			40,147,735			47,210,615	38,636,072
Net loss per share attributable to common shareholders of Biohaven Pharmaceutical Holding Company Ltd - basic and diluted (in dollars per share)	$ (2.04)			$ (1.53)			$ (8.04)	$ (4.82)