General - Basis of Presentation (Details 3) (USD $)	1 Months Ended	3 Months Ended	1 Months Ended		3 Months Ended			3 Months Ended				12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended
	Jun. 30, 2011	Mar. 31, 2013	Sep. 30, 2012 Restricted stock and restricted stock units Chief executive officer	Aug. 31, 2012 Dividend equivalent rights	Mar. 31, 2013 Dividend equivalent rights	Mar. 31, 2012 Dividend equivalent rights	Feb. 08, 2012 Dividend equivalent rights	Mar. 31, 2013 Dividend equivalent rights Chief Executive Officer and certain full-time employees	Mar. 31, 2013 Long-Term Incentive Plan	Mar. 31, 2012 Long-Term Incentive Plan	May 31, 2012 Long-Term Incentive Plan	Dec. 31, 2010 Long-Term Incentive Plan Performance award based on the EBITDA performance of the Company in 2011 and 2012 Key employees	Mar. 31, 2013 Long-Term Incentive Plan Performance award based on the EBITDA performance of the Company in 2012-2015	Dec. 31, 2011 Long-Term Incentive Plan Performance award based on the EBITDA performance of the Company in 2012-2015 Key employees	Mar. 31, 2013 Long-Term Incentive Plan Stock, restricted stock and restricted stock units	Mar. 31, 2012 Long-Term Incentive Plan Stock, restricted stock and restricted stock units	Mar. 31, 2013 Long-Term Incentive Plan Stock options	Mar. 31, 2012 Long-Term Incentive Plan Stock options	Mar. 31, 2013 Employee Stock Purchase Plan	Mar. 31, 2012 Employee Stock Purchase Plan	Mar. 31, 2013 Employee Stock Purchase Plan Stock options	Mar. 31, 2012 Employee Stock Purchase Plan Stock options
Details of stock benefit plans
Potential award grant based on achievement of performance criteria (in shares)												1,456,000		1,325,000
Modified EBITDA for an additional performance award													$ 500,000,000
Unrecognized compensation expense (in dollars)													96,000,000		1,600,000		17,300,000
Shares
Non-vested balance at the beginning of the period (in shares)															347,000
Forfeited (in shares)			(41,000)												(1,000)
Non-vested balance at the end of the period (in shares)															346,000
Weighted Average Grant Date Fair Value Per Share (in dollars per share)
Non-vested shares at the beginning of the period (in dollars per share)															$ 19.46
Granted (in dollars per share)																$ 45.82
Forfeited (in dollars per share)															$ 16.25
Non-vested shares at the end of the period (in dollars per share)															$ 19.48
Total grant date fair value of the stock awards granted (in dollars)																66,700,000
Vested (in shares)																0
Weighted-average period over which unrecognized compensation cost is expected to be recognized															1 year 4 months 20 days		2 years 9 months 14 days
Unvested stock options outstanding (in shares)							5,000,000
Dividend equivalent rights threshold for accumulated accrued dividend distribution (in shares)					1,000
Additional options granted by Board of Directors (in shares)				1,000,000				100,000
Number of shares of common stock that may be issued under the Plan											9,666,666								1,000,000
Maximum number of shares of common stock authorized to be issued under the Plan									14,066,666
Share-based compensation general disclosures
Stock-based compensation expense		7,097,000				0			7,000,000	16,900,000									100,000	100,000
Stock-based compensation for dividend equivalent rights									$ 2,000,000	$ 0
Percentage of the market value of common stock at beginning or end of the offering period for shares eligible to be purchased																			90.00%
Successive offering period under Plan																			6 months
Stock split ratio	2
Weighted-average assumptions used to estimate the fair value of purchase rights
Risk-free interest rate (as a percent)																	1.20%	1.23%			0.12%	0.06%
Expected term																	6 years 3 months	6 years 3 months			6 months	6 months
Expected volatility (as a percent)																	39.22%	44.20%			26.66%	45.37%
Expected dividend yield (as a percent)																	5.26%	4.60%			5.64%	0.58%
Shares available for grant (in shares)									3,039,000										959,000