Cash, Cash Equivalents, and Investments - Summary of Amortized Cost and Fair Value of Short-term and Long-term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	$ 49,526	$ 32,774
Due after one year, through two years	9,171	$ 9,296
Amortized Cost
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	49,526
Due after one year, through two years	9,171
Due after two years	0
Total short-term and long-term investments	58,697
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	49,512
Due after one year, through two years	9,185
Due after two years	0
Total short-term and long-term investments	$ 58,697