Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Goodwill, gross	$ 413,700,000		$ 413,700,000
Change in goodwill allocation, description	Effective in the first quarter of 2020, the Company (i) reorganized its commercial operations and moved responsibility for and reporting of RAYOS to the inflammation segment and (ii) renamed the orphan and rheumatology segment the orphan segment.  As of March 31, 2020, this resulted in a $3.2 million increase in the Company’s allocation of goodwill to its inflammation segment and a corresponding decrease in the goodwill allocated to the orphan segment.
Accumulated goodwill impairment losses	$ 0
Amortization expense of developed technology	58,575,000	$ 57,417,000
Developed Technology [Member] | Disposal Group, Not Discontinued Operations [Member] | MIGERGOT Transaction [Member]
Finite-Lived Intangible Assets [Line Items]
Write off in net book value			$ 17,000,000.0
TEPEZZA [Member] | Developed Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Capitalized payments of intangible assets	105,200,000
Inflammation [Member]
Finite-Lived Intangible Assets [Line Items]
Increase (decrease) in allocation of goodwill	3,200,000
Orphan [Member]
Finite-Lived Intangible Assets [Line Items]
Increase (decrease) in allocation of goodwill	$ (3,200,000)