Cash, Cash Equivalents, and Short-Term Investments - Summary of Cost and Estimated Fair Value of Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Short-term Investments [Abstract]
Amortized Cost of short-term investments, Due within one year	$ 22,144
Amortized Cost of short-term investments, Due within two years	13,259
Short-term investments, Amortized Cost	35,403	38,373
Estimated fair value of short-term investments, Due within one year	22,159
Estimated fair value of short-term investments, Due within two years	13,236
Short-term investments, Estimated Fair Value	$ 35,395	$ 38,381	[1]

[1] The Condensed Consolidated Balance Sheet as of December 31, 2013 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements.