Indebtedness - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended						9 Months Ended				8 Months Ended	9 Months Ended			1 Months Ended	9 Months Ended			4 Months Ended	9 Months Ended
	Nov. 04, 2011 Copal	Sep. 30, 2012 2007 Facility	Sep. 28, 2007 2007 Facility	Sep. 30, 2012 2007 Facility Minimum	Sep. 30, 2012 2007 Facility Maximum	Sep. 30, 2012 Commercial Paper	Oct. 03, 2007 Commercial Paper	Sep. 30, 2012 Series 2005-1 Notes	Sep. 30, 2005 Series 2005-1 Notes	Dec. 31, 2010 Series 2005-1 Notes	Sep. 30, 2012 Senior Notes 7.61 Percent Due September 30th 2005	Sep. 07, 2007 Series 2007-1 Notes	Sep. 30, 2012 Series 2007-1 Notes	Sep. 30, 2012 2010 Senior Notes	Sep. 30, 2012 2012 Senior Notes	Apr. 18, 2012 2012 Facility	Sep. 30, 2012 2012 Facility	Sep. 30, 2012 2012 Facility Minimum	Sep. 30, 2012 2012 Facility Maximum	May 07, 2008 2008 Term Loan	Sep. 30, 2012 2008 Term Loan	May 07, 2008 2008 Term Loan Minimum	May 07, 2008 2008 Term Loan Maximum
Debt Instrument [Line Items]
Date the credit facility was entered		Sep. 28, 2007															Apr. 18, 2012
Date of expiry of credit facility		Sep. 27, 2012															Apr. 17, 2017
Senior unsecured revolving credit facility			$ 1,000,000,000				$ 1,000,000,000									$ 1,000,000,000
Interest on borrowings under Term Loan		LIBOR plus a premium that could range from 16.0 to 40.0 basis points															LIBOR plus a premium that can range from 77.5 basis points to 120 basis points			LIBOR plus a margin that can range from 125 basis points to 175 basis points
Quarterly facility fees		4.0 to 10.0 basis points per annum															10 basis points of the facility amount to 17.5 basis points
Debt instrument term (in years)			5 years						10 years			10 years				5 years				5 years
Interest rate, LIBOR marginal basis points				0.16%	0.40%													0.775%	1.20%			1.25%	1.75%
Facility quarterly fee, basis points per annum				0.04%	0.10%													0.10%	0.175%
Debt to EBITDA ratio not to exceed at the end of any fiscal quarter													The Company must also not permit its Debt/EBITDA ratio to exceed 4.0 to 1.0 at the end of any fiscal quarter.				Debt to EBITDA Ratio of not more than 4 to 1 at the end of any fiscal quarter.				Debt/EBITDA ratio of not more than 4.0 to 1.0 at the end of any fiscal quarter.
Debt to EBITDA ratio		4.0															4
Utilization fee		5.0 basis points on borrowings outstanding when the aggregate amount outstanding exceeded 50% of the total facility
Financial covenants to be maintained at the end of any fiscal quarter		Debt/EBITDA ratio of not more than 4.0 to 1.0
Facility utilization fee on outstanding amount		0.05%
Maturity date of CP Notes (in days)						397 days
Date of agreement with the lenders for the five year senior unsecured term loan								Sep. 30, 2005					Sep. 07, 2007	Aug. 19, 2010	Aug. 20, 2012						May 07, 2008
Debt, aggregate principal amount								300,000,000			300,000,000		300,000,000	500,000,000	500,000,000					150,000,000
Senior Unsecured Notes, interest								4.98%			7.61%		6.06%	5.50%	4.50%
Maturity date of Senior Unsecured Notes								Sep. 30, 2015					Sep. 07, 2017	Sep. 01, 2020	Sep. 01, 2022
Debt to EBITDA ratio													4.0								4.0
Prepayment and purchase feature of Senior Unsecured Notes													The Company may prepay the Series 2007-1 Notes, in whole or in part, at any time at a price equal to 100% of the principal amount being prepaid, plus accrued and unpaid interest and a Make Whole Amount.	The Company may prepay the 2010 Senior Notes, in whole or in part, at any time at a price equal to 100% of the principal amount being prepaid, plus accrued and unpaid interest and a Make-Whole Amount.	The Company may prepay the 2012 Senior Notes, in whole or in part, at any time at a price equal to 100% of the principal amount being prepaid, plus accrued and unpaid interest and a Make-Whole Amount.
Issuance of additional principal amount of Senior Notes within five years from time to time													500,000,000
Percentage of principal amount being prepaid, plus accrued and unpaid interest														100.00%	100.00%
Percentage of principal amount, plus accrued and unpaid interest to the date of purchase														101.00%	101.00%
Minimum amount for default on senior notes payable														50,000,000	50,000,000
Minimum percentage for default on senior notes payable														Upon the occurrence and during the continuation of an event of default under the 2010 Indenture, the notes may become immediately due and payable either automatically or by the vote of the holders of more than 25% of the aggregate principal amount of all of the notes then outstanding.	Upon the occurrence and during the continuation of an event of default under the Indenture, the 2012 Senior notes may become immediately due and payable either automatically or by the vote of the holders of more than 25% of the aggregate principal amount of all of the notes then outstanding.
Minimum percentage of aggregate principal amount of all notes														25.00%	25.00%
Non-interest bearing note issued	14,200,000
Notes due and repayment, description	(i) the fourth anniversary date of the note or (ii) within a time frame set forth in the acquisition agreement relating to the resolution of certain income tax uncertainties pertaining to the transaction. Otherwise, the Company must repay any amount outstanding on the earlier of (i) two business days subsequent to the exercise of the put/call option to acquire the remaining shares of Copal or (ii) the tenth anniversary date of the issuance of the note.
Interest rate swaps total notional amount										$ 300,000,000										$ 150,000,000