Debt - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended									1 Months Ended	12 Months Ended
	Jun. 30, 2009	Dec. 31, 2011	Dec. 31, 2009	Apr. 15, 2009	Mar. 31, 2009 Senior Notes 7.85 Percent Due 2009	May 31, 2011 Senior Notes, 5.000 Percent Due 2021	Dec. 31, 2011 Private Placement Debt Due May 2012	Dec. 31, 2011 CPT	Dec. 31, 2011 Maximum	Dec. 31, 2011 Other Credit Facilities	Apr. 30, 2011 Credit Facility	Dec. 31, 2011 Credit Facility
Debt Disclosure [Line Items]
Aggregate principal amount						$ 500,000,000
Debt, interest rate						5.00%
Debt, maturity year						2021
Previous revolving credit facility											800,000,000
Credit facility maximum borrowing capacity										74,200,000	700,000,000
Credit facility expiration date											2016-04-28
Credit facility interest rate, before the addition of LIBOR											1.75%
Remaining availability under the Credit Facility												528,000,000
Remaining availability under the Credit Facility limited by leverage ratio												480,300,000
Debt agreement financial covenant, leverage ratio that may not exceeded by reported date									3.5
Compliance with debt agreement financial covenants		We were in compliance with all financial covenants in our debt agreements as of December 31, 2011.
Line of credit facility, amount outstanding										14,100,000
Long-term debt, outstanding							105,000,000
Long-term debt, maturity date							2012-05
Outstanding aggregate principal of Notes					133,900,000
Notes redemption price per $1,000 of principal outstanding				1,035.88
Debt tender offer				1,000
Loss due to early extinguishment of debt	(4,800,000)		(4,804,000)
Unamortized deferred financing fees write off	100,000
Previously unrecognized swap gains	300,000
Cash paid for redemption and other costs associated with the purchase	5,000,000
Capital lease obligation cost								22,700,000
Accumulated amortization								5,100,000
Future minimum lease payments		17,900,000
Imputed interest		$ 2,100,000