Financing - Additional Information (Detail) (USD $)	12 Months Ended							1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Line of Credit	Aug. 31, 2011 Line of Credit	Dec. 31, 2010 Term Loan	Dec. 31, 2011 Maximum	Dec. 31, 2010 Master Notes Senior Unsecured Notes, 3.81 Percent, Due May 2018	Dec. 31, 2010 Master Notes Senior Unsecured Notes, 4.60 Percent, Due May 2021 [Member]	Nov. 30, 2009 Master Notes Interest Rate Lock Commitments
Line of Credit Facility [Line Items]
Revolving loan facility, maximum capacity				$ 350,000,000	$ 250,000,000
Maturity date				2016-08				2018-05	2021-05
Term Loan outstanding						200,000,000
Repayment of term loan	100,000,000
Issuance of senior notes								25,000,000	75,000,000
Interest rate for purchase agreement								3.81%	4.60%
Gain on interest rate lock settlement										251,000
Deferred tax related to interest rate lock settlement	(16,946,000)	(16,888,000)	13,573,000							149,000
Capital lease obligations	7,253,000
Capital lease obligations, current	2,653,000
Letter of credit outstanding	4,496,000
Total debt outstanding	$ 731,319,000
Aggregate repurchase obligation, amount, percentage							15.00%