Note 7 - Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statutory federal rate applied to income before income tax expense	$ 67,647	$ 36,992	$ 23,012
Current year permanent items	2,408	1,830	1,192
State and local taxes, net of federal tax benefit	7,889	5,056	2,831
Change in valuation allowance	(1,457)	(151)	(369)
Reserve for uncertain tax positions	757	(698)	(581)
Rate change due to enactment of tax reform	(145,997)	0	0
Other items, net	79	389	363
Income tax (benfit) expense as recorded	$ (68,674)	$ 43,418	$ 26,448
Effective income tax (benefit) expense rate	(35.50%)	41.10%	40.20%