Employee Benefit Plans - Stock Options (Details) (USD $) In Millions, except Share data, unless otherwise specified		12 Months Ended						5 Months Ended
	Dec. 31, 2013	Dec. 31, 2013 Non-vested Stock	Dec. 31, 2013 Performance Shares [Member]	Dec. 31, 2012 Individual Arrangements	Dec. 31, 2013 Stock Options	Dec. 31, 2012 Stock Options	Dec. 31, 2011 Stock Options	Dec. 31, 2013 Ameristar Individual Arrangements
Share-based Compensation Arrangement by Share-based Payment Award
Share Based Compensation Arrangement by Share Based Payment Award Cumulative Shares Issued	6,600,000
Options Outstanding
Options outstanding at January 1, 2013					5,519,345
Options outstanding, weighted average exercise price, beginning balance					$ 11.78
Options granted, shares				850,000	1,251,159			198,000
Options granted, weighted average exercise price					$ 21.64
Options exercised, shares					(880,031)
Options exercised, weighted average exercise price					$ 11.48
Options cancelled or forfeited, shares					(381,227)
Options cancelled or forfeited, weighted average exercise price					$ 10.88
Options outstanding at December 31, 2013					5,509,246	5,519,345
Options outstanding, weighted average exercise price, ending balance					$ 14.01	$ 11.78
Options outstanding, weighted average remaining contractual term (years)					5 years 3 months 30 days
Options outstanding, aggregate intrinsic value					$ 66.4
Options Vested and Expected to Vest [Abstract]
Vested or expected to vest at December 31, 2013, shares					2,176,609
Vested or expected to vest at December 31, 2013, weighted average exercise price					$ 15.55
Vested or expected to vest at December 31, 2013, weighted average remaining contractual term (years)					5 years 11 months 9 days
Vested or expected to vest at December 31, 2013, aggregate intrinsic value					22.7
Options - Additional Disclosures [Abstract]
Options exercisable at December 31, 2013, shares					2,636,839
Options exercisable at December 31, 2013, weighted average exercise price					$ 12.62
Options exercisable at December 31, 2013, weighted average remaining contractual term (years)					4 years 8 months 10 days
Options exercisable at December 31, 2013, aggregate intrinsic value					35.6
Weighted-average grant date fair value					$ 10.63	$ 5.06	$ 6.65
Total intrinsic value of options exercised					9.2	0.5	3.0
Net proceeds from exercise of stock options					10.1	1.5	3.7
Unamortized compensation costs		$ 11.4			$ 18.9
Unamortized compensation costs period of recognition (years)		2 years			2 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		714,958	442,540					74,000