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	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	$ 32,774	$ 9,101
Due after one year, through two years	9,296	12,023
Amortized Cost
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	32,774
Due after one year, through two years	9,048
Due after two years	248
Total short-term and long-term investments	42,070
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	33,773
Due after one year, through two years	9,032
Due after two years	248
Total short-term and long-term investments	$ 43,053