Note 2 - Summary of Significant Accounting Policies (Details Textual)	1 Months Ended	12 Months Ended
	Nov. 30, 2021	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($)	Jul. 08, 2015 USD ($) shares
Self-Insurance Coverage, Medical Insurance Claims, Limit		$ 125,000	$ 125,000
Self Insurance, Coverage for Medical Claims, Aggregate Deductible		57,500	57,500
Advertising Expense		19,100,000	9,300,000	$ 22,400,000
Marketing Expense		9,800,000	3,500,000	6,000,000.0
Foreign Financial Institutions, Actual Deposits		1,000,000.0	7,200,000
Required Escrow Deposit Amount, Maximum		32,000,000
Cash Reserve Deposit Required and Made		$ 10,500,000	1,900,000
Number of Vessels Owned		10
Goodwill, Impairment Loss		$ 0	0
License Agreement, Term of Contract (Year)	20 years
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)		0	0
Impairment, Long-Lived Asset, Held-for-Use, Total		0	0
Proceeds from Coronavirus Economic Relief for Transportation Services (CERTS) Act, Grant		27,000,000.0
Other Nonoperating Income (Expense), Total		15,487,000	(83,000)	(66,000)
Unrecognized Tax Benefits, Ending Balance		0	0	0	$ 298,000
Financing Receivable, Credit Loss, Expense (Reversal)		0	0	0
Ulstein Verft [Member] | National Geographic Resolution [Member] | Loans Receivable [Member]
Receivable with Imputed Interest, Face Amount				$ 4,000,000.0
Repayment of Loans Receivable, Related Parties, Percent of Principal Balance				112.00%
Legal Fees				$ 100,000
National Geographic [Member]
Number of Shares Called by Options (in shares) | shares							2,387,499
Call Options, Long Term Asset							$ 13,800,000
National Geographic Endeavour II [Member]
Value Added Tax Receivable, Current						$ 3,600,000
Fair Value, Recurring [Member]
Other Liabilities, Fair Value Disclosure		$ 0	$ 0
Office Space, Lease [Member] | Minimum [Member]
Lessee, Operating Lease, Term of Contract (Year)		1 year
Office Space, Lease [Member] | Maximum [Member]
Lessee, Operating Lease, Term of Contract (Year)		10 years
Equipment Lease [Member] | Minimum [Member]
Lessee, Operating Lease, Term of Contract (Year)		3 years
Equipment Lease [Member] | Maximum [Member]
Lessee, Operating Lease, Term of Contract (Year)		6 years
Grant [Member]
Other Nonoperating Income (Expense), Total		$ 15,400,000
Trade Names [Member]
Finite-Lived Intangible Asset, Useful Life (Year)		15 years
Customer Lists [Member]
Finite-Lived Intangible Asset, Useful Life (Year)		5 years