Organization and Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended		9 Months Ended
	Jan. 01, 2019 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) Segment	Sep. 30, 2018	Dec. 31, 2018 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities		$ 1,726,754,000		$ 1,726,754,000		$ 1,918,239,000
Senior secured notes		250,000,000.0		$ 250,000,000.0
Number of business segment | Segment				1
Accounts receivable for expense reimbursements from collaboration partner		41,205,000		$ 41,205,000		43,213,000
Operating lease, right-of-use assets		134,888,000		134,888,000		0
Operating lease, lease liabilities		154,417,000		154,417,000
Cumulative effect adjustment to accumulated deficit			$ 12,577,000
Effective income tax rate					0.40%
Tax provision on unrealized gain on available-for-sale securities, offset by benefit in continuing operations		$ 300,000		$ 1,300,000
India
Organization And Summary Of Significant Accounting Policies [Line Items]
Effective income tax rate		33.00%		33.00%
ASC 842
Organization And Summary Of Significant Accounting Policies [Line Items]
Operating lease, right-of-use assets	$ 83,500,000
Operating lease, lease liabilities	96,200,000
Cumulative effect adjustment to accumulated deficit	$ 0
Collaboration Partner
Organization And Summary Of Significant Accounting Policies [Line Items]
Accounts receivable for expense reimbursements from collaboration partner		$ 27,700,000		$ 27,700,000		$ 24,200,000