Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2019	Jul. 08, 2015
Contract with Customer, Liability, Current	$ 123,489,000	$ 123,489,000	$ 112,238,000
Health Care Organization, Stop Loss Insurance Recoveries		125,000	100,000
Self Insurance, Coverage for Medical Claims, Aggregate Deductible		57,500	57,500
Advertising Expense		16,900,000	16,400,000	$ 14,700,000
Marketing Expense		5,400,000	6,300,000	5,500,000
Foreign Financial Institutions, Actual Deposits	6,400,000	6,400,000	4,100,000
Required Escrow Deposit Amount, Maximum	30,000,000	30,000,000
Cash Reserve Deposit Required and Made	1,500,000	1,500,000	1,500,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		(671,000)
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	600,000	600,000
Unrecognized Tax Benefits, Ending Balance	298,000	298,000	421,000	447,000	$ 473,000
Subsequent Event [Member] | Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset							$ 6,400,000
Operating Lease, Liability, Total							$ 6,400,000
License Agreement with National Geographic [Member]
License Agreement Asset	3,600,000	3,600,000	6,500,000
National Geographic [Member]
Number of Shares Called by Options								2,387,499
Call Options, Long Term Asset								$ 13,800,000
Other Noncurrent Assets [Member]
Derivative Asset, Current	700,000	700,000
Other Noncurrent Liabilities [Member]
Unrecognized Tax Benefits, Ending Balance	300,000	300,000	400,000
Foreign Exchange Forward [Member]
Derivative, Notional Amount	32,800,000	32,800,000	21,500,000
Foreign Exchange Forward [Member] | Fair Value, Inputs, Level 2 [Member] | Accounts Payable and Accrued Liabilities [Member]
Derivative Liability, Current	1,300,000	1,300,000
Foreign Exchange Forward [Member] | Fair Value, Inputs, Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member]
Derivative Asset, Current			1,000,000
Interest Rate Cap [Member]
Derivative Asset, Notional Amount	$ 100,000,000	$ 100,000,000
Office Space, Lease [Member] | Minimum [Member]
Lessee, Operating Lease, Term of Contract	1 year	1 year
Office Space, Lease [Member] | Maximum [Member]
Lessee, Operating Lease, Term of Contract	10 years	10 years
Equipment Lease [Member] | Minimum [Member]
Lessee, Operating Lease, Term of Contract	3 years	3 years
Equipment Lease [Member] | Maximum [Member]
Lessee, Operating Lease, Term of Contract	6 years	6 years
National Geographic Endeavour II [Member]
Property, Plant and Equipment, Useful Life					1 year	7 years
Value Added Tax Receivable, Current	$ 2,700,000	$ 2,700,000	3,500,000	$ 3,600,000
Trade Names [Member]
Finite-Lived Intangible Asset, Useful Life		15 years
Customer Lists [Member]
Finite-Lived Intangible Asset, Useful Life		5 years
Contract Liabilities [Member]
Contract with Customer, Liability, Current	$ 70,900,000	$ 70,900,000	$ 62,100,000