Note 14 - Income Taxes - Federal and State Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current federal income tax													$ 53,290	$ 46,758	$ 32,384
Current state income tax													13,733	11,020	7,114
Total current													67,023	57,778	39,498
Deferred federal income tax benefit													(5,523)	(6,642)	(7,494)
Deferred state income tax benefit													(105)	(87)	(46)
Total deferred													(5,628)	(6,729)	(7,540)
Total income tax expense	$ 16,429	$ 15,484	$ 15,069	$ 14,413	$ 13,485	$ 13,054	$ 12,776	$ 11,734	$ 9,347	$ 8,054	$ 7,618	$ 6,939	$ 61,395	$ 51,049	$ 31,958