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	Sep. 30, 2014	Dec. 31, 2013
Financial Assets:
Total financial assets	$ 238,590	$ 315,429
Financial Liabilities:
Total financial liabilities	(68)
Fair Value, Inputs, Level 1
Financial Assets:
Total financial assets	13,588	57,296
Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	225,002	258,133
Financial Liabilities:
Total financial liabilities	(68)
Money market funds
Financial Assets:
Total financial assets	13,588	57,296
Money market funds | Fair Value, Inputs, Level 1
Financial Assets:
Total financial assets	13,588	57,296
Corporate notes and commercial paper
Financial Assets:
Total financial assets	164,006	182,472
Corporate notes and commercial paper | Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	164,006	182,472
U.S. government agency securities
Financial Assets:
Total financial assets	60,996	75,289
U.S. government agency securities | Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	60,996	75,289
Foreign currency forward contracts
Financial Assets:
Total financial assets		372
Financial Liabilities:
Fair value of financial liabilities measured on a recurring basis	(68)
Foreign currency forward contracts | Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets		372
Financial Liabilities:
Fair value of financial liabilities measured on a recurring basis	$ (68)