Cash, cash equivalents, and investments - Summary of Amortized Cost and Fair Value of Short-term and Long-term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	$ 22,890	$ 9,101
Due after one year, through two years	10,918	12,023
Amortized Cost [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	22,890
Due after one year, through two years	10,918
Total short-term and long-term investments	33,808
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due in less than one year	22,903
Due after one year, through two years	10,923
Total short-term and long-term investments	$ 33,826