STOCK-BASED COMPENSATION PLANS (Details) (USD $)	3 Months Ended
	Mar. 31, 2013 plan	Mar. 31, 2012
Stock-based compensation plans
Number of stock-based employee compensation plans	2
Non-cash stock-based compensation expense	$ 1,800,000	$ 1,200,000
Total unrecognized compensation cost related to non-vested stock awards	19,500,000
Weighted average period over which compensation cost is expected to be recognized	2 years
Stock option
Stock-based compensation plans
Total intrinsic value of awards exercised	13,800,000	55,900,000
Total amount of cash received from the exercise of options	4,300,000	13,500,000
Tax benefit associated with the exercise of awards recorded to additional capital	4,700,000	19,300,000
Total Options
Outstanding at the beginning of the period (in shares)	3,159,542
Granted (in shares)	10,017
Exercised (in shares)	(449,872)
Forfeited (in shares)	(16,667)
Outstanding at the end of the period (in shares)	2,703,020
Exercisable at the end of the period (in shares)	896,748
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 18.96
Granted (in dollars per share)	$ 42.19
Exercised (in dollars per share)	$ 9.34
Forfeited (in dollars per share)	$ 27.74
Outstanding at the end of the period (in dollars per share)	$ 20.60
Exercisable at the end of the period (in dollars per share)	$ 14.66
Weighted Average Remaining Contractual Term (In Years)
Outstanding at the end of the period	6 years 1 month 6 days
Exercisable at the end of the period	5 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding at the end of the period	50,527,000
Exercisable at the end of the period	22,079,000
Weighted-average date fair values of options granted (in dollars per share)	$ 12.97	$ 9.89
Fair value of options vested	$ 1,000,000	$ 1,700,000
Stock option | Minimum
Stock-based compensation plans
Vesting period	4 years
Expiration period	7 years
Stock option | Maximum
Stock-based compensation plans
Vesting period	5 years
Expiration period	10 years
2011 Stock Plan | Class A common stock
Stock-based compensation plans
Number of shares authorized for issuance	8,500,000
Number of shares reserved for every share granted that are Full Share Awards	1.8
Number of shares available for grant for every share forfeited that are Full Share Awards	1.8
2007 Stock Plan
Stock-based compensation plans
Granted (in shares)	0