Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands		3 Months Ended
	Apr. 13, 2020 USD ($)	Mar. 31, 2020 USD ($) Segment	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Oct. 05, 2015 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities		$ 1,531,782		$ 1,603,981
Senior secured notes		$ 254,800
Tax provision on unrealized gain on available-for-sale securities, offset by benefit in continuing operations			$ 1,100
Number of business segment | Segment		1
Accounts receivable for expense reimbursements from collaboration partner		$ 42,031		36,802
Operating lease, right-of-use assets		133,901		134,177
7.75% Senior Secured Notes Due October 2020 | Senior Notes
Organization And Summary Of Significant Accounting Policies [Line Items]
Senior secured notes					$ 250,000
7.75% Senior Secured Notes Due October 2020 | Senior Notes | Subsequent Event
Organization And Summary Of Significant Accounting Policies [Line Items]
Repayments of long term debt, including interest	$ 254,800
NKTR - 181
Organization And Summary Of Significant Accounting Policies [Line Items]
Write off of prepayment		19,700
Purchase commitment, remaining minimum amount committed		25,500
Collaboration Partner
Organization And Summary Of Significant Accounting Policies [Line Items]
Accounts receivable for expense reimbursements from collaboration partner		10,900		12,800
BMS Collaboration Agreement
Organization And Summary Of Significant Accounting Policies [Line Items]
Accounts receivable for expense reimbursements from collaboration partner		$ 31,200		$ 24,000