Investments and Fair Value Measurements - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013 Y	Dec. 31, 2012
Investments And Fair Value Measurements [Line Items]
Cash and cash equivalents	$ 712,694,000	$ 477,073,000
Long-term investments, contractual maturity period, low, years	1
Long-term investments, contractual maturity period, high, years	2
Cost of investment in private company	2,000,000	2,000,000
U.S. Treasury and other government agencies percentage of fixed income available-for-sale securities	46.00%
Corporate bonds percentage of fixed income available-for-sale securities	31.00%
Commercial paper percentage of available-for-sale securities	15.00%
Non-U.S. Government securities percentage of available-for-sale securities	8.00%
Money market funds percentage of available-for-sale securities	0.00%
Cash equivalents included in available-for-sale securities	10,900,000
Investment Maturity Period Maximum	3 months
United States
Investments And Fair Value Measurements [Line Items]
Cash equivalents and investments	490,900,000
Foreign Tax Authority
Investments And Fair Value Measurements [Line Items]
Cash equivalents and investments	$ 462,900,000