Shareholders' Equity - Changes in Shareholders' Equity (Details) - USD ($) $ 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (35,466)	$ 121,958	$ (7,424)	$ 186,741	$ 97,011	$ 150,920	$ (7,424)	$ 150,920
Issuance of common shares, net of offering costs			282,833	21,221	281,100
Issuance of common shares under equity incentive plan	3,460	11,748	2,607			1,065
Issuance of common shares as payment for assets				5,646
Exercise of related party warrants					1,998
Exercise of stock options				1,564	148
Exercise of stock options (shares)							1,700,357
Non-cash share-based compensation expense	14,565	11,762	16,879	9,971	17,554	7,330
Net loss	(196,628)	(180,934)	(172,937)	(106,167)	(211,070)	(62,304)	$ (550,499)	(379,541)
Other comprehensive income	251			0			251	0
Ending balance	(213,818)	(35,466)	121,958	118,976	186,741	97,011	(213,818)	118,976
Biohaven Shareholders' Equity (Deficit)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(35,466)	121,958	(7,424)				(7,424)
Issuance of common shares, net of offering costs			282,833
Issuance of common shares under equity incentive plan	3,460	11,748	2,607
Non-cash share-based compensation expense	14,565	11,762	16,879
Net loss	(195,189)	(180,934)	(172,937)
Other comprehensive income	251
Ending balance	(212,379)	(35,466)	121,958				(212,379)
Common Shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 1,199,005	$ 1,175,139	$ 881,426	$ 844,966	$ 556,345	$ 554,384	$ 881,426	$ 554,384
Beginning balance (in shares)	59,525,565	58,387,948	52,385,283	51,501,614	44,282,994	44,197,549	52,385,283	44,197,549
Issuance of common shares, net of offering costs			$ 282,833	$ 21,221	$ 281,100
Stock issued (shares)			5,555,554	525,000	6,976,745
Issuance of common shares under equity incentive plan	$ 6,379	$ 23,866	$ 10,880			$ 1,961
Issuance of common shares under equity incentive plan (shares)	182,215	1,137,617	447,111			85,445
Issuance of common shares as payment for assets				$ 5,646
Issuance of common shares as payment for assets (in shares)				100,000
Exercise of related party warrants					$ 7,201
Exercise of related party warrants (shares)					215,000
Exercise of stock options				$ 2,756	$ 320
Exercise of stock options (shares)				91,070	26,875
Ending balance	$ 1,205,384	$ 1,199,005	$ 1,175,139	$ 874,589	$ 844,966	$ 556,345	$ 1,205,384	$ 874,589
Ending balance (in shares)	59,707,780	59,525,565	58,387,948	52,217,684	51,501,614	44,282,994	59,707,780	52,217,684
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 91,773	$ 92,129	$ 83,523	$ 58,717	$ 46,538	$ 40,104	$ 83,523	$ 40,104
Issuance of common shares under equity incentive plan	(2,919)	(12,118)	(8,273)			(896)
Exercise of related party warrants					(5,203)
Exercise of stock options				(1,192)	(172)
Non-cash share-based compensation expense	14,565	11,762	16,879	9,971	17,554	7,330
Ending balance	103,419	91,773	92,129	67,496	58,717	46,538	103,419	67,496
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,326,244)	(1,145,310)	(972,373)	(716,942)	(505,872)	(443,568)	(972,373)	(443,568)
Net loss	(195,189)	(180,934)	(172,937)	(106,167)	(211,070)	(62,304)
Ending balance	(1,521,433)	(1,326,244)	(1,145,310)	$ (823,109)	$ (716,942)	$ (505,872)	(1,521,433)	$ (823,109)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	0	0				0
Other comprehensive income	251
Ending balance	251	0	0				251
Non-controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	0	0				0
Net loss	(1,439)
Ending balance	$ (1,439)	$ 0	$ 0				$ (1,439)