Stock-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity participation plans	Two
Weighted-average fair value of options granted	$ 20.31	$ 18.53	$ 15.88
Total intrinsic value for options exercised	$ 49.0	$ 12.7	$ 17.8
Cash received from option exercises	32.0	15.2	15.1
Stock option total intrinsic value closing price	$ 70.98
Total unrecognized compensation cost related to unvested stock options	17.5
Weighted average period to recognize cost, years	2 years 5 months 1 day
Total fair value of shares vested	9.0	9.0	8.7
Total unrecognized compensation expense related to unvested restricted stock	9.1
Weighted-average period, expected to be recognized, years	3 years 2 months 19 days
Non-cash compensation expense relating to 2008 and 1999 purchase plans	0.2	0.2	0.2
Non-cash compensation capitalized to fixed and intangible assets	0.2	0.2	0.1
2010 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares remaining available for future issuance under the plan	13,500,000
2010 Plan [Member] | Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum issuance of shares	15,000,000
2010 Plan [Member] | Aggregate number of share [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum issuance of granted	7,500,000
2008 Plan [Member] | Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares remaining available for future issuance under the plan	380,045
Common stock were reserved for purchase under the purchase plan	500,000
Percentage of purchase plan price per share equal to the fair market value	85.00%
Class A common stock were issued under the purchase plan	23,724	30,942
Cash proceeds from issuance of shares under the purchase plan	$ 1.1	$ 1.0
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum contractual life of options and restricted stock units	7 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum contractual life of options and restricted stock units	10 years