Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	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	165,100,000		165,100,000
Total gross unrealized loss position			400,000
Recognize impairment charges	0	0	0	0
Investments in marketable securities	0		0		0
Net gain related to forward contracts	1,200,000	300,000	600,000	300,000
Assets	1,448,153,000		1,448,153,000		1,299,194,000
Liabilities	619,347,000		619,347,000		572,226,000
Level 3 [Member]
Financial Instruments [Line Items]
Assets	0		0		0
Liabilities	$ 0		$ 0		$ 0