Note 24 - 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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Interest income	$ 183,869	$ 176,866	$ 167,520	$ 159,700	$ 155,640	$ 154,078	$ 135,629	$ 130,804
Interest expense	38,428	31,782	27,489	24,357	22,593	20,882	18,277	18,690	$ 122,056		$ 80,442		$ 81,200
Net interest income	145,441	145,084	140,031	135,343	133,047	133,196	117,352	112,114	565,899		495,709		417,870
Provision/(reversal) for loan losses		(1,500)		(3,000)				(2,500)	(4,500)		(2,500)		(15,650)
Net-interest income after reversal for loan losses	145,441	146,584	140,031	138,343	133,047	133,196	117,352	114,614	570,399		498,209		433,520
Non-interest income	10,795	7,835	7,767	5,310	10,466	12,961	6,152	6,718	31,707	[1]	36,297	[1]	33,370	[1]
Non-interest expense	74,395	65,964	63,088	60,971	66,407	61,248	56,658	51,886	264,419		236,199		224,690
Income before income tax expense	81,841	88,455	84,710	82,682	77,106	84,909	66,846	69,446
Total income tax expense, amount	17,193	18,698	11,046	18,866	51,166	35,163	15,431	20,505	65,802		122,265		67,101
Net income	$ 64,648	$ 69,757	$ 73,664	$ 63,816	$ 25,940	$ 49,746	$ 51,415	$ 48,941	$ 271,885		$ 176,042		$ 175,099
Basic (in dollars per share)	$ 0.80	$ 0.86	$ 0.91	$ 0.79	$ 0.32	$ 0.62	$ 0.64	$ 0.61	$ 3.35		$ 2.19		$ 2.21
Diluted (in dollars per share)	$ 0.80	$ 0.85	$ 0.90	$ 0.78	$ 0.32	$ 0.61	$ 0.64	$ 0.61	$ 3.33		$ 2.17		$ 2.19

[1] There were no adjustments to the Company's financial statements recorded as a result of the adoption of ASC 606. For comparability, the Company has adjusted prior period amounts to conform to the periods presentation.