Incentive Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2011 USD ($) Year	Dec. 31, 2010 USD ($)		Dec. 31, 2009 USD ($)		Dec. 31, 2011 Maximum	Dec. 31, 2011 Annual Incentive Plan, 2007 Annual Plan	Dec. 31, 2007 Annual Incentive Plan, 2007 Annual Plan	Dec. 31, 2011 Directors Plan	Dec. 31, 2011 Stock Options	Dec. 31, 2011 Performance-Based Restricted Stock	Dec. 31, 2011 Performance-Based Restricted Stock Maximum USD ($)	Dec. 31, 2010 Performance-Based Restricted Stock Maximum USD ($)	Dec. 31, 2009 Performance-Based Restricted Stock Maximum USD ($)	Dec. 31, 2011 Performance-Based Restricted Stock Minimum USD ($)	Dec. 31, 2010 Performance-Based Restricted Stock Minimum USD ($)	Dec. 31, 2009 Performance-Based Restricted Stock Minimum USD ($)	Dec. 31, 2011 Time-Lapse Restricted Stock and Restricted Stock Units USD ($)	Dec. 31, 2010 Time-Lapse Restricted Stock and Restricted Stock Units USD ($)	Dec. 31, 2009 Time-Lapse Restricted Stock and Restricted Stock Units USD ($)	Dec. 31, 2011 Performance Based Units USD ($)	Dec. 31, 2011 Employee Stock Purchase Plan USD ($)	Dec. 31, 2010 Employee Stock Purchase Plan USD ($)	Dec. 31, 2009 Employee Stock Purchase Plan USD ($)	Dec. 31, 2011 Savings Related Share Option Plan (SOP)	Dec. 31, 2011 Savings Related Share Option Plan (SOP) Maximum GBP (£)	Dec. 31, 2011 Savings Related Share Option Plan (SOP) Minimum GBP (£)	Dec. 31, 2011 Savings Related Share Option Plan (SOP) SOP plans with holding periods ending in December 2009 USD ($)	Dec. 31, 2011 Savings Related Share Option Plan (SOP) SOP plans with holding periods ending in August 2010 USD ($)	Dec. 31, 2011 Savings Related Share Option Plan (SOP) SOP plans with holding periods ending in April 2011 USD ($)	Dec. 31, 2011 Savings Related Share Option Plan (SOP) SOP plans with holding periods ending in May 2012 USD ($)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Salary that can be withhold by eligible employee for stock purchase																						10.00%
Stock purchase price, percentage of the fair value of the stock																						90.00%			90.00%
Employee Stock purchase plan, termination date																						The ESPP will terminate on the earlier of the date that employees have purchased all 980,000 authorized shares or June 30, 2017.
Employee stock purchase plan, authorized shares							5,745,000	6,700,000														980,000
Employee stock purchases, shares																						34,612	44,361	51,271
Maximum number of shares available for issuance, annual rate								1.00%
Employee stock purchases, per share																						$ 56.08	$ 51.97	$ 44.73
Number of shares remained available																						321,322
Compensation costs estimation																						Compensation costs related to the ESPP are estimated based on the value of the 10% discount and the fair value of the option that provides for the refund of participant withholdings.			Compensation costs related to the SOP plan are estimated based on the value of the 10% discount and the fair value of the option that allows the employee to receive a repayment of withholdings plus credited interest.
Compensation costs related to the ESPP																						$ 328,000	$ 357,000	$ 623,000
Fair value per share issued under ESPP																						$ 8.60	$ 7.51	$ 11.47
Unvested share-based compensation arrangements, compensation costs to be expensed	55,100,000
Unvested share-based compensation arrangements, number of years compensation costs to be expensed	2
Proceeds from exercise of stock options and employee stock purchase plans	15,551,000	42,995,000	[1]	12,746,000	[1]
Income tax benefits realized for the tax deductions from option exercises	8,775,000	15,896,000		6,035,000
Option granted to date, term of years						7 years	7 years
Employee stock purchase plan, vesting scheme							Under the 2007 Long-Term Plan, one-half of each grant is exercisable after two years and the remainder after three years.		Under the Directors Plan, one-third of each grant is exercisable after each of the first three years.
Stock-based compensation, fair value assumption model										Black-Scholes pricing model	Monte Carlo valuation model
Total intrinsic value of options exercised	28,145,000	49,929,000		17,932,000
Compensation expense for incentive plans	33,035,000	25,171,000		23,073,000
Granted restricted stock, valuation												$ 64.89	$ 50.95	$ 44.94	$ 38.94	$ 42.38	$ 41.18	$ 52.66	$ 52.49	$ 43.95
Percentage of targeted amounts paid in cash and awards based on achivement, minimum																					0.00%
Percentage of targeted amounts paid in cash and awards based on achivement, maximum																					200.00%
Total expense related to performance award																					871,000
Monthly salary that can be withhold by eligible employee for stock purchase																										£ 250	£ 5
Fair value per share of SOP plans																												$ 19.57	$ 19.90	$ 23.77	$ 22.85

[1] Reclassified to conform to current presentation.