Collaboration, Development and License Agreements - Serum License Agreement (Details) - USD ($)	1 Months Ended		12 Months Ended
	Sep. 30, 2019	Jul. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Total revenue			$ 1,022,000	$ 2,757,000
Deferred revenue, current			14,602,000	$ 22,000
Deferred revenue, noncurrent			5,000,000
Capitalized contract cost, Current			1,537,000
Capitalized contract cost, Noncurrent			$ 526,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Royalty payments			4.00%
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Royalty payments			6.00%
License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Capitalized contract costs			$ 2,100,000
Total revenue			0
Deferred revenue, current			14,600,000
Deferred revenue, noncurrent			5,000,000
Capitalized incremental costs of obtaining the License Agreement			2,100,000
Capitalized contract cost, Current			1,500,000
Capitalized contract cost, Noncurrent			526,000
Licenses and know-how
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue			14,500,000
Development support services
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue			79,000
Research and Development Option
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue			892,000
Manufacturing rights option
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue			$ 4,100,000
Products in EU
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Royalty payments			20.00%
License Agreement with SIBV
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received		$ 5,000,000
Issuance costs from equity allocation			$ 376,000
License Agreement with SAMR
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Buy back manufacturing rights			5,000,000
Upfront payment received	$ 15,000,000	$ 5,000,000	42,500,000
License Agreement and Option Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Proceeds from sale of restricted common stock and upfront payment			22,500,000
Fair value of net proceeds			5,000,000
Fair value of gross proceeds			5,400,000
Deferred revenue			19,600,000
Deferred revenue based on upfront payments			15,000,000
Deferred revenue from equity allocation			4,600,000
Capitalized contract costs			2,100,000
Issuance costs from equity allocation			441,000
Direct costs related to license agreement			1,700,000
Capitalized incremental costs of obtaining the License Agreement			$ 2,100,000
Serum International B.V. ("SIBV")
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Issuance of common stock (in shares)		801,820
Issuance of common stock		$ 10,000,000
Restricted common stock | Serum International B.V. ("SIBV")
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Issuance of common stock (in shares)		801,820
Issuance of common stock		$ 10,000,000