Stock-Based Compensation (Detail) - Summary Of Changes In SARs Outstanding (USD $)	9 Months Ended
	Sep. 30, 2013
Weighted Average Remaining Contractual Term [Roll Forward]
Granted	2 years 3 months 18 days
Stock appreciation rights (SARs)
SARs [Roll Forward]
Outstanding at December 31, 2012 (in shares)	2,000,000
Granted (in shares)	400,000
Forfeited (in shares)	0
Exercised (in shares)	(400,000)
Outstanding at September 30, 2013 (in shares)	2,000,000	[1],[2]
Vested and exercisable at September 30, 2013 (in shares)	1,000,000	[1]
Per Share Weighted- Average Exercise Price [Roll Forward]
Outstanding at December 31, 2012 (in Dollars per share)	$ 24.59
Granted (in Dollars per share)	$ 49.37
Forfeited (in Dollars per share)	$ 0.00
Exercised (in Dollars per share)	$ 18.80
Outstanding at September 30, 2013 (in Dollars per share)	$ 30.11	[1],[2]
Vested and exercisable at September 30, 2013 (in Dollars per share)	$ 21.00	[1]
Per Share Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding at December 31, 2012 (in dollars per share)	$ 9.04
Granted (in Dollars per share)	$ 14.88
Forfeited (in Dollars per share)	$ 0.00
Exercised (in Dollars per share)	$ 7.02
Outstanding at September 30, 2013 (in Dollars per share)	$ 10.46	[1],[2]
Vested and exercisable at September 30, 2013 (in Dollars per share)	$ 7.98	[1]
Weighted Average Remaining Contractual Term [Roll Forward]
Outstanding at December 31, 2012	4 years 36 days
Granted	6 years 4 months 13 days
Outstanding at September 30, 2013	4 years 2 months 5 days	[1],[2]
Vested and exercisable at September 30, 2013	3 years 2 months 1 day	[1]

[1] Total SARs outstanding had an intrinsic value of $59.3 million. SARs vested and exercisable had an intrinsic value of $39.8 million.

[2] As of September 30, 2013, 1.0 million of the SARs outstanding were unvested. The Company expects that substantially all of these unvested awards will vest in future periods.