Note 9 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	35.00%
Deferred Tax Liabilities, Net	$ 84,157	$ 76,981
Deferred Tax Assets, Valuation Allowance	1,219	1,219
Liability for Uncertainty in Income Taxes, Current	2,800	3,200
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	800	900
Income Tax Expense (Benefit)	10,386	21,822	$ 14,774
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	2,400	2,700
Interest and Penalties Recognized for Uncertain Tax Positions [Member]
Income Tax Expense (Benefit)	(100)	(200)	$ (100)
Deferred Tax Assets Excludes State Net Operating Loss Carry Forwards [Member]
Deferred Tax Assets, Valuation Allowance	0	0
State and Local Jurisdiction [Member]
Tax Credit Carryforward, Amount	300
Operating Loss Carryforwards	$ 78,100
State and Local Jurisdiction [Member] | Earliest Tax Year [Member]
Open Tax Year	2013
State and Local Jurisdiction [Member] | Latest Tax Year [Member]
Open Tax Year	2016
State and Local Jurisdiction [Member] | Deferred Tax Assets Related to State Net Operating Loss Carry Forwards [Member]
Deferred Tax Assets, Valuation Allowance	$ 1,200	$ 1,200
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Tax Credit Carryforward, Amount	7,600
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Alternative Minimum Tax Credit Carry Forward [Member]
Tax Credit Carryforward, Amount	$ 300
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Earliest Tax Year [Member]
Open Tax Year	2013
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Latest Tax Year [Member]
Open Tax Year	2016