Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class A Common Stock and Class C Capital Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Class A common stock and Class C capital stock equivalents excluded from calculations of diluted net income (loss) per share	32,695	24,040	29,595
Class A Common Stock and Class C Capital Stock | Option Awards | Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Class A common stock and Class C capital stock equivalents excluded from calculations of diluted net income (loss) per share	27,998	19,993	16,607
Class A Common Stock and Class C Capital Stock | Restricted Stock Awards and Restricted Stock Units | Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Class A common stock and Class C capital stock equivalents excluded from calculations of diluted net income (loss) per share	4,262	3,607	3,453
Class A Common Stock | 2.75% Convertible Senior Notes Due 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Class A common stock and Class C capital stock equivalents excluded from calculations of diluted net income (loss) per share	435	440	9,535