Cash and Investments - Schedule of Cash and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 852,467	$ 742,217	$ 131,303	$ 465,523
Marketable securities	0	245,033
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	33,985	16,995
U.S. Government and Government Agency Debt Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	19,987	39,989
Marketable securities		144,986
Corporate Debt Securities [Member]
Cash and Cash Equivalents [Line Items]
Marketable securities		100,047
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	123,382	162,495
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	439,330	362,587
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 235,783	$ 160,151