Revenues (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Capitalized Contract Cost [Line Items]
Total revenues	$ 34,138	$ (33,688)	$ 175,605	$ 2,032,750	$ 2,517,413	$ 3,186,850	$ 2,806,631	$ 2,439,767	$ 2,208,805	$ 10,950,661	$ 9,493,849
Refunds	95,800				9,800				95,800	9,800
Contract liabilities	124,800				1,700,000				124,800	1,700,000
Contract assets	53,700				55,500				53,700	55,500
Commissions, transportation and other
Capitalized Contract Cost [Line Items]
Capitalized contract costs	$ 1,100				$ 163,200				$ 1,100	163,200
Minimum
Capitalized Contract Cost [Line Items]
Duration of cruises									2 days
Maximum
Capitalized Contract Cost [Line Items]
Duration of cruises									24 days
Port Costs
Capitalized Contract Cost [Line Items]
Total revenues									$ 125,000	$ 666,800	$ 611,400