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, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	$ 45,620	$ 50,254
Due after one year, through two years	6,260	$ 8,525
Amortized Cost
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	45,620
Due after one year, through two years	6,260
Due after two years	0
Total short-term and long-term investments	51,880
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	45,581
Due after one year, through two years	6,260
Due after two years	0
Total short-term and long-term investments	$ 51,841