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, 2013	Dec. 31, 2012
Financial Assets:
Total financial assets	$ 215,411	$ 127,125
Fair Value, Inputs, Level 1
Financial Assets:
Total financial assets	54,930	43,303
Fair Value, Inputs, Level 2
Financial Assets:
Total financial assets	160,481	83,822
Fair Value, Inputs, Level 3
Financial Assets:
Total financial assets
Money market funds
Financial Assets:
Fair value of financial assets measured on a recurring basis	54,930	43,303
Money market funds | Fair Value, Inputs, Level 1
Financial Assets:
Fair value of financial assets measured on a recurring basis	54,930	43,303
Money market funds | Fair Value, Inputs, Level 2
Financial Assets:
Fair value of financial assets measured on a recurring basis
Money market funds | Fair Value, Inputs, Level 3
Financial Assets:
Fair value of financial assets measured on a recurring basis
Corporate notes and commercial paper
Financial Assets:
Fair value of financial assets measured on a recurring basis	103,065	64,425
Corporate notes and commercial paper | Fair Value, Inputs, Level 1
Financial Assets:
Fair value of financial assets measured on a recurring basis
Corporate notes and commercial paper | Fair Value, Inputs, Level 2
Financial Assets:
Fair value of financial assets measured on a recurring basis	103,065	64,425
Corporate notes and commercial paper | Fair Value, Inputs, Level 3
Financial Assets:
Fair value of financial assets measured on a recurring basis
U.S. government agency securities
Financial Assets:
Fair value of financial assets measured on a recurring basis	57,150	19,346
U.S. government agency securities | Fair Value, Inputs, Level 1
Financial Assets:
Fair value of financial assets measured on a recurring basis
U.S. government agency securities | Fair Value, Inputs, Level 2
Financial Assets:
Fair value of financial assets measured on a recurring basis	57,150	19,346
U.S. government agency securities | Fair Value, Inputs, Level 3
Financial Assets:
Fair value of financial assets measured on a recurring basis
Foreign currency forward contracts
Financial Assets:
Fair value of financial assets measured on a recurring basis	266	51
Foreign currency forward contracts | Fair Value, Inputs, Level 1
Financial Assets:
Fair value of financial assets measured on a recurring basis
Foreign currency forward contracts | Fair Value, Inputs, Level 2
Financial Assets:
Fair value of financial assets measured on a recurring basis	266	51
Foreign currency forward contracts | Fair Value, Inputs, Level 3
Financial Assets:
Fair value of financial assets measured on a recurring basis
Convertible Preferred Stock
Financial Liabilities:
Fair value of financial liabilities measured on a recurring basis		683
Convertible Preferred Stock | Fair Value, Inputs, Level 1
Financial Liabilities:
Fair value of financial liabilities measured on a recurring basis
Convertible Preferred Stock | Fair Value, Inputs, Level 2
Financial Liabilities:
Fair value of financial liabilities measured on a recurring basis
Convertible Preferred Stock | Fair Value, Inputs, Level 3
Financial Liabilities:
Fair value of financial liabilities measured on a recurring basis		$ 683