Debt - Summary of Debt Instruments (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended						3 Months Ended		1 Months Ended	3 Months Ended				1 Months Ended		1 Months Ended		1 Months Ended		3 Months Ended	12 Months Ended
	Mar. 31, 2013 Installment	Dec. 31, 2012	Mar. 31, 2013 Revolving A Facility [Member]	Mar. 31, 2013 Revolving B Facility [Member]	Mar. 31, 2013 Minimum [Member] Eurodollar Rate [Member]	Mar. 31, 2013 Maximum [Member] Eurodollar Rate [Member]	Mar. 31, 2013 Term Note Payable-Domestic, June 22, 2011 [Member]	Mar. 31, 2013 Term Note Payable-Domestic, June 22, 2011 [Member] Revolving Credit Facility [Member]	Nov. 06, 2012 Term Note Payable-Domestic, June 22, 2011 [Member] Revolving Credit Facility [Member]	Nov. 06, 2012 Term Note Payable-Domestic, June 22, 2011 [Member] Term Loan [Member]	Mar. 31, 2013 Term Note Payable-Domestic, June 22, 2011 [Member] Term Loan Facility [Member]	Nov. 06, 2012 Term Note Payable-Domestic, June 22, 2011 [Member] Term Loan Facility [Member]	Mar. 31, 2013 Term Note Payable-Domestic, June 22, 2011 [Member] Line of Credit [Member]	Mar. 31, 2013 Term Note Payable-Domestic, June 22, 2011 [Member] Swing Line Loans [Member]	Nov. 06, 2012 Term Note Payable-Domestic, June 22, 2011 [Member] Minimum [Member]	Mar. 31, 2013 Term Note Payable-Domestic, June 22, 2011 [Member] Minimum [Member]	Nov. 06, 2012 Term Note Payable-Domestic, June 22, 2011 [Member] Maximum [Member]	Mar. 31, 2013 Term Note Payable-Domestic, June 22, 2011 [Member] Maximum [Member]	Mar. 31, 2012 Amended And Restated [Member]	Mar. 31, 2013 Amended And Restated [Member] Swing Line Loans [Member]	Mar. 31, 2013 Commercial Paper [Member]	Dec. 31, 2012 Commercial Paper [Member]
Debt Instrument [Line Items]
Line of credit facility, increase additional borrowings										$ 250					$ 150		$ 250
Increase borrowing limit on revolving line of credit			815.0	35.0					850.0			550.0	20.0	20.0	600.0		850.0			110.0
Debt maturity date								Mar. 20, 2018			Mar. 01, 2018
United Kingdom entities as designated borrowers																			Two
Interest on the line of credit, sum of rate plus					1.25%	2.25%										0.25%		1.25%
Principal payments on term loan							7.5
Current purchase limit under the securitization facility	500
Securitization facility termination date	Feb. 03, 2014
Program fee rate																					0.22%	0.24%
Program fee variable rate																					0.675%	0.75%
Unused facility fee payable rate	0.30%	0.35%
Deferred payment	11.3	11.3
Contingent earn-out payment	$ 3.8	$ 5.2
Number of installments for earn out payments	2