Summary of Liability and Equity Components of Notes (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long term convertible debt	$ 25,367	$ 64,279
2.75% Convertible Senior Notes due 2020 (2013 Notes)
Debt Instrument [Line Items]
Principal amount of senior convertible notes outstanding	30,303	79,903
Unamortized discount of liability component	(4,890)	(15,477)
Unamortized debt issuance costs	(46)	(147)
Long term convertible debt	25,367	64,279
Carrying value of equity component, net of issuance costs	$ 31,178	$ 31,178
Remaining amortization period of discount on the liability component	3 years 3 months 19 days	4 years