Note 11 - Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2015
Current:
Federal									$ 59,433	$ 28,788	$ 31,587
State									28,278	22,364	26,396
Total Current									87,711	51,152	57,983
Deferred:
Federal									31,818	11,775	3,738
State									2,736	4,174	(1,734)
Total Deferred									34,554	15,949	2,004
Total income tax expense	$ 51,166	$ 35,163	$ 15,431	$ 20,505	$ 16,345	$ 15,808	$ 12,273	$ 22,675	$ 122,265	$ 67,101	$ 59,987	$ 59,987