Commitments - Summary of Lease Arrangements of Company Facilities (Detail)	6 Months Ended
	Jun. 30, 2019 ft² Option
Vacaville, CA [Member] | Manufacturing [Member]
Property Subject To Or Available For Operating Lease [Line Items]
Approximate Square Feet	24,634
Expiration	Lease expires 2023
Lease expiration year	2023
Birmingham, AL [Member] | Office, Laboratory and Manufacturing [Member]
Property Subject To Or Available For Operating Lease [Line Items]
Approximate Square Feet	21,540
Expiration	Lease expires 2021 (with two options to renew the lease term for an additional five years each after the current lease expires)
Lease expiration year	2021
Lease renewal term	5 years
Number of renewal option for lease | Option	2
Cupertino, CA [Member] | Office, Laboratory and Manufacturing [Member]
Property Subject To Or Available For Operating Lease [Line Items]
Lease expiration year	2024
Lease renewal term	5 years
Cupertino, CA [Member] | Office, Laboratory and Manufacturing [Member] | Lease Amendment [Member]
Property Subject To Or Available For Operating Lease [Line Items]
Approximate Square Feet	30,149
Expiration	Lease expires 2024 (with an option to renew for an additional five years)
Cupertino, CA [Member] | Office and Laboratory [Member]
Property Subject To Or Available For Operating Lease [Line Items]
Lease expiration year	2024
Lease renewal term	5 years
Cupertino, CA [Member] | Office and Laboratory [Member] | Lease Amendment [Member]
Property Subject To Or Available For Operating Lease [Line Items]
Approximate Square Feet	20,100
Expiration	Lease expires 2024 (with an option to renew for an additional five years)