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	Dec. 31, 2014	Dec. 31, 2013
Financial Assets:
Total financial assets	$ 371,131	$ 315,429
Fair Value, Inputs, Level 1
Financial Assets:
Total financial assets	24,915	57,296
Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	346,216	258,133
Money market funds
Financial Assets:
Total financial assets	24,915	57,296
Money market funds | Fair Value, Inputs, Level 1
Financial Assets:
Total financial assets	24,915	57,296
Corporate notes and commercial paper
Financial Assets:
Total financial assets	226,047	182,472
Corporate notes and commercial paper | Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	226,047	182,472
U.S. government agency securities
Financial Assets:
Total financial assets	120,169	75,289
U.S. government agency securities | Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	120,169	75,289
Foreign Exchange Forward
Financial Assets:
Total financial assets		372
Foreign Exchange Forward | Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets		$ 372