Note 23 - Quarterly Results of Operations (Unaudited) - Selected Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ 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, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest income	$ 130,668	$ 124,155	$ 121,902	$ 122,345	$ 119,519	$ 116,867	$ 112,386	$ 104,934
Interest expense	20,766	20,331	20,126	19,977	20,103	19,221	17,632	17,008	$ 81,200	$ 73,964	$ 75,866
Net interest income	109,902	103,824	101,776	102,368	99,416	97,646	94,754	87,926	417,870	379,742	342,781
Provision/(reversal) for loan losses			(5,150)	(10,500)	(3,000)	(1,250)	(2,150)	(5,000)	(15,650)	(11,400)	(10,800)
Net-interest income after reversal for loan losses	109,902	103,824	106,926	112,868	102,416	98,896	96,904	92,926	433,520	391,142	353,581
Non-interest income	7,961	8,811	9,057	7,541	9,350	9,156	5,619	8,549	33,370	32,674	40,527
Non-interest expense	53,503	50,737	68,879	51,571	53,533	57,471	47,585	44,131	224,690	202,720	174,313
Income before income tax expense	64,360	61,898	47,104	68,838	58,233	50,581	54,938	57,344	242,200	221,096	219,795
Income tax expense	16,345	15,808	12,273	22,675	16,787	12,098	9,738	21,364	67,101	59,987	81,965
Net income	$ 48,015	$ 46,090	$ 34,831	$ 46,163	$ 41,446	$ 38,483	$ 45,200	$ 35,980	$ 175,099	$ 161,109	$ 137,830
Basic (in dollars per share)	$ 0.61	$ 0.58	$ 0.44	$ 0.58	$ 0.51	$ 0.47	$ 0.57	$ 0.45	$ 2.21	$ 2	$ 1.73
Diluted (in dollars per share)	$ 0.60	$ 0.58	$ 0.44	$ 0.57	$ 0.51	$ 0.47	$ 0.56	$ 0.45	$ 2.19	$ 1.98	$ 1.72