Derivative Instruments - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2012 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Feb. 08, 2008 Contract	Oct. 31, 2010 Foreign Currency Forward Exchange Contracts Four [Member] USD ($)	Oct. 31, 2010 Foreign Currency Forward Exchange Contracts Four [Member] AUD	Sep. 22, 2011 Foreign Currency Forward Exchange Contracts Five [Member] USD ($)	Sep. 22, 2011 Foreign Currency Forward Exchange Contracts Five [Member] AUD	Aug. 23, 2011 Foreign Currency Forward Exchange Contracts Five [Member] USD ($)	Aug. 23, 2011 Foreign Currency Forward Exchange Contracts Five [Member] AUD
Derivative [Line Items]
Fair value of derivative instruments outstanding	$ 1,700,000	$ 1,000,000
Foreign exchange gain/(loss) on foreign currency forward exchange contracts			1,900,000
Number of foreign currency forward exchange contracts held by the Company				2
Contract amount and settlement amount	88,875,000	88,875,000			42,500,000	45,000,000	34,000,000	35,000,000	37,000,000	35,000,000
Foreign exchange gain/(loss) on foreign currency forward exchange contracts		$ 3,000,000