Investments - Fair Value of Short-Term Available-for-Sale and Trading Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	$ 140,042	$ 299,715
Fair value of short-term investments	140,042	300,715
Bankers' Acceptance Drafts [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	765	491
Time Deposits and Certificates of Deposit [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	40,672	64,989
Commercial Paper [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	9,691	53,434
Corporate Obligations [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	14,890	18,351
Municipal Bonds [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	2,099
U.S. Agency Obligations [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	71,925	162,450
Mutual Funds [Member]
Schedule of Investments [Line Items]
Fair value of short-term investments, mutual funds		$ 1,000