DEBT - Additional Information (Detail) (USD $)	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Guarantee	Dec. 31, 2011 Line of Credit	Sep. 21, 2011 Line of Credit	Dec. 31, 2010 Line of Credit	Dec. 31, 2011 $100 million Private Placement notes 5.64%, due in 2015	Dec. 31, 2010 $100 million Private Placement notes 5.64%, due in 2015	Dec. 31, 2011 $175 million Private Placement notes 3.89%, due in 2017	Dec. 31, 2010 $175 million Private Placement notes 3.89%, due in 2017	Dec. 31, 2011 $225 million Private Placement notes 4.47%, due in 2020	Dec. 31, 2010 $225 million Private Placement notes 4.47%, due in 2020
Debt Instrument [Line Items]
Maximum borrowing capacity of line of credit facility					$ 1,000,000,000	$ 850,000,000
Payments of deferred financing costs	3,740,000	5,757,000	3,635,000		3,740,000
Amended line of credit, maturity date					Sep. 21, 2016
Interest paid	43,500,000	28,600,000	24,800,000
Long-term debt, face amount								100,000,000	100,000,000	175,000,000	175,000,000	225,000,000	225,000,000
Debt, maturity date				2012-05				2015-04		2017-10		2020-10
Senior letters of credit facility, committed to outstanding letters of credit					159,100,000		184,000,000
Senior letters of credit facility, unused portion					313,000,000		490,600,000
Bank loan guaranteed on behalf of Shiraishi	6,400,000
Notes Receivable extended to Shiraishi	$ 15,200,000