Net Income (Loss) Per Share of Common Stock - Shares excluded from Computation of Diluted Net Income (Loss) per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	11,947	95,745	22,237	92,832
Stock options and employee stock purchase plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	11,859	29,814	17,440	25,817
Restricted Shares [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount		3,344	467	4,165
Restricted Stock Units (ZSUs) [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	88	62,587	4,330	62,850