Summary of Financial Assets, and Liabilities, Allocated into Level 1, Level 2, and Level 3 Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financial Assets:
Total financial assets	$ 280,098	$ 315,429
Fair Value, Inputs, Level 1
Financial Assets:
Total financial assets	25,344	57,296
Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	254,754	258,133
Money market funds
Financial Assets:
Fair value of financial assets measured on a recurring basis	25,344	57,296
Money market funds | Fair Value, Inputs, Level 1
Financial Assets:
Fair value of financial assets measured on a recurring basis	25,344	57,296
Corporate notes and commercial paper
Financial Assets:
Fair value of financial assets measured on a recurring basis	176,478	182,472
Corporate notes and commercial paper | Fair Value, Inputs, Level 2
Financial Assets:
Fair value of financial assets measured on a recurring basis	176,478	182,472
U.S. government agency securities
Financial Assets:
Fair value of financial assets measured on a recurring basis	78,031	75,289
U.S. government agency securities | Fair Value, Inputs, Level 2
Financial Assets:
Fair value of financial assets measured on a recurring basis	78,031	75,289
Foreign currency forward contracts
Financial Assets:
Fair value of financial assets measured on a recurring basis	245	372
Foreign currency forward contracts | Fair Value, Inputs, Level 2
Financial Assets:
Fair value of financial assets measured on a recurring basis	$ 245	$ 372