Organization and Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended			6 Months Ended
	Jan. 01, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jun. 30, 2018	Dec. 31, 2018 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities		$ 1,791,684,000			$ 1,791,684,000		$ 1,918,239,000
Senior secured notes		250,000,000.0			$ 250,000,000.0
Number of business segment | Segment					1
Accounts receivable from contracts with customers		12,900,000			$ 12,900,000		24,200,000
Accounts receivable for expense reimbursements from collaboration partner		37,299,000			37,299,000		43,213,000
Operating lease, right-of-use assets	$ 83,500,000	82,177,000			82,177,000		0
Operating lease, lease liabilities	96,200,000	98,571,000			98,571,000
Cumulative effect adjustment to accumulated deficit				$ 12,577,000
Effective income tax rate			0.50%			0.50%
Tax provision on unrealized gain on available-for-sale securities, offset by benefit in continuing operations		$ 400,000			$ 1,500,000
India
Organization And Summary Of Significant Accounting Policies [Line Items]
Effective income tax rate		29.00%			29.00%
ASC 842
Organization And Summary Of Significant Accounting Policies [Line Items]
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		$ 24,400,000			$ 24,400,000		$ 19,000,000.0