Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net loss		$ (23,998)	$ (47,734)	$ (63,046)	$ 84,090	$ (88,452)	$ (56,742)	$ (62,301)	$ (59,770)	$ (50,688)	$ (267,265)	$ (220,030)
Weighted-average number of shares of common stock and common stock equivalents outstanding:
Weighted-average number of shares of common stock outstanding for computing basic loss per share		64,277	61,528	54,976	54,850					58,818	48,697	42,290
Dilutive effect of outstanding stock awards and stock options after application of the treasury stock method	[1]									0	0	0
Weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for computing diluted loss per share						54,619	48,254	46,157	45,697	58,818	48,697	42,290
Net loss per share — basic and diluted						$ (1.62)	$ (1.18)	$ (1.35)	$ (1.31)	$ (0.86)	$ (5.49)	$ (5.20)

[1] For the year ended December 31, 2017, stock options, RSAs, RSUs and SARs to purchase approximately 9.4 million shares of common stock, respectively, were excluded from the net loss per share calculation as their effect would have been anti-dilutive. The Company accounts for the effect of the 2024 Notes on diluted net loss per share using the if-converted method as they may be settled in cash or shares at the Company’s option. The 2024 Notes have no effect on diluted net loss per share until the Company’s stock price exceeds the conversion price of $73.42 per share. In the period of conversion, the 2024 Notes will have no impact on diluted net loss if they are settled in cash and will have an impact on diluted loss per share if the Notes are settled in shares upon conversion. For the years ended 2016 and 2015, stock options, RSAs and SARs to purchase approximately 5.7 million and 6.8 million shares of common stock, respectively, were excluded from the net loss per share calculation as their effect would have been anti-dilutive.