Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012 Derivative	Jun. 30, 2013	Jun. 30, 2012 Derivative	Dec. 31, 2012
Financial Instruments [Line Items]
Financial instruments including money market funds maturities period			90 days
Maximum maturities period of long-term marketable securities			3 years
Minimum maturities period of long-term marketable securities			1 year
Maximum maturities period of short-term marketable securities			12 months
Minimum maturities period of short-term marketable securities			90 days
Material realized gains or losses related to sales of marketable securities	$ 0	$ 0	$ 0	$ 0
Total fair value of marketable securities	332,500,000		332,500,000
Total gross unrealized loss position			1,200,000
Recognize impairment charges	0	0	0	0	0
Investments in marketable securities	0		0		0
Net gain related to forward contracts	100,000		700,000
Derivative number of instruments entered into or settled during period		0		0
Assets	1,455,585,000		1,455,585,000		1,299,194,000
Liabilities	603,626,000		603,626,000		572,226,000
Level 3 [Member]
Financial Instruments [Line Items]
Assets	0		0		0
Liabilities	$ 0		$ 0		$ 0