Fair Value Measurements and Derivative Instruments - Nonrecurring (Details) $ in Thousands		3 Months Ended				9 Months Ended			12 Months Ended
		Dec. 31, 2020 USD ($) ship		Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) ship	Sep. 30, 2021 USD ($) ship		Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity method investments, impairment					$ 39,700
Total, impairment				$ 83,900				$ 1,200,000
Indefinite-life intangible assets		$ 321,500							$ 321,500
Number of cruise ships | ship						60
Valuation, Income And Cost Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of cruise ships | ship					2
Disposal Group, Held-for-sale, Not Discontinued Operations | Azamara
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of ships held for sale | ship		3
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Indefinite-life intangible asset, impairment	[1]								30,800
Long-lived assets, impairment						$ 40,643	[2]		727,063	[3]
Right-of-use assets, impairment	[4]								65,909
Equity method investments, impairment	[5]								39,735
Total, impairment						40,643			1,439,715
Nonrecurring | Silversea Cruises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Silversea Goodwill, impairment	[6]								576,208
Nonrecurring | Total Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Indefinite-life intangible asset	[1]	$ 318,700							318,700
Long-lived assets		577,193	[3]			0	[2]		577,193	[3]
Right-of-use assets	[4]	67,265							67,265
Equity method investments	[5]	0							0
Total		1,471,736				0			1,471,736
Nonrecurring | Total Carrying Amount | Silversea Cruises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Silversea Goodwill	[6]	508,578							508,578
Nonrecurring | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Indefinite-life intangible asset	[1]	318,700							318,700
Long-lived assets		577,193	[3]			0	[2]		577,193	[3]
Right-of-use assets	[4]	67,265							67,265
Equity method investments	[5]	0							0
Total		1,471,736				0			1,471,736
Nonrecurring | Total Fair Value | Silversea Cruises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Silversea Goodwill	[6]	508,578							508,578
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Indefinite-life intangible asset	[1]	318,700							318,700
Long-lived assets		577,193	[3]			0	[2]		577,193	[3]
Right-of-use assets	[4]	67,265							67,265
Equity method investments	[5]	0							0
Total		$ 1,471,736				$ 0			$ 1,471,736
Nonrecurring | Level 3 | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Indefinite-lived intangible assets, measurement input		13.25%							13.25%
Nonrecurring | Level 3 | Royalty fee percentage
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Indefinite-lived intangible assets, measurement input		3.00%							3.00%
Nonrecurring | Level 3 | Silversea Cruises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Silversea Goodwill	[6]	$ 508,578							$ 508,578
Nonrecurring | Level 3 | Silversea Cruises | Weighted average cost of capital
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, measurement input		12.75%							12.75%

[1] Amount represents the Silversea Cruises trade name which makes up the majority of our indefinite-life intangible assets, totaling $321.5 million. We estimated the fair value of the Silversea Cruises trade name using a discounted cash flow model and the relief-from-royalty method and used a discount rate of 13.25%. Significant inputs in performing the fair value assessment for the trade name were (i) forecasted net revenues, primarily the timing of returning to normalized operations, occupancy rates from existing and expected ship deliveries, including options, and terminal growth rate; (ii) the royalty rate of 3.0%; and (iii) weighted average cost of capital (i.e., discount rate). The fair value of the Silversea Cruises trade name was estimated as of March 31, 2020, the date the asset was last impaired.

[2] During the quarter ended June 30, 2021, certain construction in progress assets were impaired due to a reduction in scope or the decision to not complete the projects. The impairment was calculated based on orderly liquidation values. The fair value of these assets was estimated as of June 30, 2021.

[3] Impairments primarily relate to certain vessels during 2020. In addition, certain construction in progress projects generated impairments during the quarter ended September 30, 2020 and quarter ended December 31, 2020. For the vessels impaired during the quarter ended March 31, 2020, we estimated the fair value of two of our vessels using a blended indication from the income and cost approaches and the fair value of the remaining vessels was estimated primarily based on their orderly liquidation values. For the vessels impaired during the quarter ended June 30, 2020, we estimated the fair value of the vessels using a modified market approach based on the carrying values and orderly liquidation values of the vessels. For the vessels impaired during the quarter ended December 31, 2020, we estimated the fair value of the three Azamara vessels using a market approach. A significant input in performing the fair value assessments for these vessels was management's expected use of the vessels, which takes into consideration forecasted operating results. During the quarter ended September 30, 2020 and quarter ended December 31, 2020, construction in progress assets were impaired due to a reduction in scope or the decision to not complete the projects. The impairment was calculated based on orderly liquidation values. The fair value of these assets was estimated as of the date the asset was last impaired.

[4] Impairments to our right-of-use assets relate to certain of our berthing arrangements and a ship operating lease. We estimated the fair value of the berthing arrangements using estimated projected discounted cash flows and the fair value of the ship operating lease was estimated using a market approach. The fair value of the berthing arrangements was estimated as of March 31, 2020, the date these assets were last impaired. A significant input in performing the fair value assessments for these assets was our expected passenger headcount. The fair value of the ship operating lease was estimated as of December 31, 2020, the date this asset was last impaired, and significant inputs in performing the fair value assessment using the market approach for this asset were the expected rate of return and remaining lease payments.

[5] We estimated the fair value of our other than temporarily impaired equity-method investments using a discounted cash flow model. A significant input in performing the fair value assessments for these assets was forecasted operating results for these investments. The fair value of these equity-method investments was estimated as of March 31, 2020, the date these assets were last impaired. For further information on our equity method investments, refer to Note 6. Other Assets.

[6] We estimated the fair value of the Silversea Cruises reporting unit using a probability-weighted discounted cash flow model in combination with a market based valuation approach. The principal assumptions used in the discounted cash flow model were (i) the timing of our return to service, changes in market conditions and port or other restrictions; (ii) forecasted net revenues, primarily the timing of returning to normalized operations, occupancy rates from existing and expected ship deliveries, including options, and terminal growth rate; and (iii) weighted average cost of capital (i.e., discount rate). The discounted cash flow model used our 2020 projected operating results as a base. To that base we added future years’ cash flows through 2030 assuming multiple revenue and expense scenarios that reflect the impact of different global economic environments for this period on the Silversea Cruises' reporting unit. We assigned a probability to each revenue and expense scenario. We discounted the projected cash flows using rates specific to the Silversea Cruises' reporting unit based on its weighted-average cost of capital, which was determined to be 12.75%. The fair value of Silversea Cruises’ goodwill was estimated as of March 31, 2020, the date the asset was last impaired.