Fair Value of Financial Instruments - Summary of Carrying Amount and Estimated Fair Value of Convertible Notes (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Carrying Amounts And Estimated Fair Values Of Financial Instruments [Line Items]
Debt instrument interest rate	1.25%	1.25%
Carrying Amount	$ 419,426	$ 356,602
Convertible Debt
Carrying Amounts And Estimated Fair Values Of Financial Instruments [Line Items]
Debt instrument interest rate			1.25%
Carrying Amount	218,176	212,852
Estimated Fair Value	$ 258,998	$ 261,903