Acquisition of Annapurna - Summary of Identifiable Intangible Assets Acquired (Detail) - Annapurna Therapeutics SAS [Member] $ in Thousands	May 11, 2016 USD ($)
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 16,650
IPR&D [Member]
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	16,650
IPR&D [Member] | Alpha-1 Antitrypsin Deficiency [Member]
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	12,150
IPR&D [Member] | Hereditary Angiodema [Member]
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 4,500