Note 13 - Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Federal tax provision at statutory rate	$ 91,947	$ 73,673	$ 58,026
State taxes, net of federal income tax benefit	9,357	6,526	$ 3,141
Equity investment basis difference	11,048	1,422
Non-deductible items	882	1,766	$ 1,010
Permanent differences related to the employee stock purchase program	156	68	55
Net change in valuation allowance	(3,303)	(4,121)	(554)
General business credits	(29,093)	(4,002)	(440)
Other	(1,289)	(377)	(664)
Income tax provision	$ 79,705	$ 74,955	$ 60,574