Summary of Significant Accounting Policies (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended			3 Months Ended			6 Months Ended		3 Months Ended	6 Months Ended																	3 Months Ended		6 Months Ended
	Jul. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Retama Partners	Jun. 30, 2013 Other Properties	Jun. 30, 2012 Other Properties	Jun. 30, 2013 Other Properties	Jun. 30, 2012 Other Properties	Jun. 30, 2013 Antidilutive securities	Jun. 30, 2013 Antidilutive securities	Jun. 30, 2013 Estimate of Fair Value Measurement [Member] Fair Value, Measurements, Recurring	Dec. 31, 2012 Estimate of Fair Value Measurement [Member] Fair Value, Measurements, Recurring	Jun. 30, 2013 Estimate of Fair Value Measurement [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Estimate of Fair Value Measurement [Member] Fair Value, Measurements, Nonrecurring [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member]	Jun. 30, 2013 Ameristar	Jun. 30, 2012 Ameristar	Jun. 30, 2013 Ameristar	Jun. 30, 2012 Ameristar	Aug. 07, 2013 Ameristar Subsequent Event	Aug. 05, 2013 Senior Notes Due 2021 Subsequent Event	Jun. 30, 2013 Senior Notes Due 2021 Ameristar	Jun. 30, 2013 Ameristar	Jun. 30, 2013 Credit Facility	Dec. 31, 2012 Credit Facility	Jun. 30, 2013 Term Loan	Dec. 31, 2012 Term Loan	Jun. 30, 2013 Credit Facility Ameristar	Jun. 30, 2013 Credit Facility Term Loan Ameristar
Business Acquisition, Share Price																														$ 26.50		$ 26.50
Purchase price																														$ 2,800,000,000		$ 2,800,000,000
Credit Facility, Maximum Borrowing Capacity																														1,040,000,000		1,040,000,000						410,000,000				1,000,000,000
Debt Instrument, Interest Rate, Stated Percentage																																			6.38%	7.50%
Debt Instrument, Consent Fee																														19.00		19.00					9,800,000.00
Debt Instrument, Face Amount																														1,000		1,000			850,000,000					325,000,000			1,600,000,000
Business Acquisition, Credit on Project Costs																																		37,000,000
Business Acquisition, Percentage of Bondholders Consent Fees																														50.00%
Business Acquisition, Funds Required																														1,140,000,000
Business Acquisition, Percentage of Voting Interests Acquired							75.50%
Deferred Compensation														800,000	1,000			800,000	0			0	0			0	0
Held-to-maturity Securities		14,800,000		14,800,000		14,400,000
Held-to-maturity Securities, Fair Value																30,100,000	14,400,000			0	0			26,700,000	14,400,000			3,400,000	0
Promissory Notes		9,000,000		9,000,000		4,000,000
Promissory Notes, Fair Value																15,900,000	4,000,000			0	0			15,900,000	4,000,000			0	0
Long-term Debt		1,459,500,000		1,459,500,000		1,440,500,000																																20,000,000	0	318,300,000	319,700,000
Long-term Debt, Fair Value																1,523,000,000	1,532,100,000			0	0			1,523,000,000	1,532,100,000			0	0
Land Not Used In Operations		35,600,000		35,600,000
Land and land improvements		298,800,000		298,800,000		291,900,000
Buildings, riverboats and improvements		1,561,500,000		1,561,500,000		1,539,300,000
Furniture, fixtures and equipment		536,200,000		536,200,000		528,000,000
Construction in progress		88,800,000		88,800,000		47,900,000
Land, buildings, vessels and equipment, gross		2,485,300,000		2,485,300,000		2,407,100,000
Less: accumulated depreciation		(750,000,000)		(750,000,000)		(711,100,000)
Goodwill, Acquired During Period							3,300,000
Intangible Asset, Acquired During Period							5,000,000
Customer Loyalty Program Liability		13,300,000		13,300,000		11,500,000
Complimentary Revenues, Food and Beverage		19,800,000	16,200,000	38,700,000	32,200,000
Complimentary Revenues, Lodging		8,900,000	7,900,000	17,100,000	15,400,000
Complimentary Revenues, Other		3,300,000	2,500,000	6,300,000	4,700,000
Total promotional allowances		32,000,000	26,600,000	62,100,000	52,300,000
Promotional allowance costs included in gaming expense		23,000,000	19,500,000	46,300,000	38,500,000
Gaming taxes		79,300,000	76,000,000	160,400,000	152,400,000
Pre-opening and development costs		17,208,000	4,212,000	24,769,000	6,970,000			600,000	4,200,000	1,500,000	7,000,000																			16,600,000	0	23,300,000	0
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount												1.6	1.4
Stock Repurchase Program, Authorized Amount	100,000,000
Treasury Stock, Shares, Acquired		4.4
Purchase of treasury shares				51,000,000
Prior Period Reclassification Adjustment		$ 2,700,000