Debt and Average Interest Rates on Debt Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Debt Disclosure [Line Items]
Contractual debt obligations	$ 1,309,087	$ 707,472
Less: Current maturities	(1,168)	(18)
Short-term borrowings	(3,694)	(4,933)
Long-term debt	1,304,225	702,521
Commercial Paper
Debt Disclosure [Line Items]
Debt, average interest rate	1.26%
Maturity (Year)	2016
Contractual debt obligations	3,497
Revolving credit facilities
Debt Disclosure [Line Items]
Debt, average interest rate	2.04%
Maturity (Year)	2016
Contractual debt obligations	168,500	97,500
Private Placement | Fixed Rate
Debt Disclosure [Line Items]
Debt, average interest rate	5.65%
Contractual debt obligations	400,000	400,000
Private Placement | Fixed Rate | Minimum
Debt Disclosure [Line Items]
Maturity (Year)	2013
Private Placement | Fixed Rate | Maximum
Debt Disclosure [Line Items]
Maturity (Year)	2017
Private Placement | Floating Rate
Debt Disclosure [Line Items]
Debt, average interest rate	0.99%
Contractual debt obligations	205,000	205,000
Private Placement | Floating Rate | Minimum
Debt Disclosure [Line Items]
Maturity (Year)	2012
Private Placement | Floating Rate | Maximum
Debt Disclosure [Line Items]
Maturity (Year)	2016
Public Placement | Fixed Rate
Debt Disclosure [Line Items]
Debt, average interest rate	5.00%
Maturity (Year)	2021
Contractual debt obligations	500,000
Capital Lease Obligations
Debt Disclosure [Line Items]
Debt, average interest rate	3.72%
Maturity (Year)	2025
Contractual debt obligations	15,788
Debt, Other
Debt Disclosure [Line Items]
Debt, average interest rate	3.04%
Contractual debt obligations	$ 16,302	$ 4,972
Debt, Other | Minimum
Debt Disclosure [Line Items]
Maturity (Year)	2012
Debt, Other | Maximum
Debt Disclosure [Line Items]
Maturity (Year)	2021