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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Interest income	$ 191,226	$ 197,831	$ 192,449	$ 187,761	$ 183,869	$ 176,866	$ 167,520	$ 159,700
Interest expense	50,015	50,831	49,070	44,445	38,428	31,782	27,489	24,357	$ 194,361		$ 122,056		$ 80,442
Net interest income	141,211	147,000	143,379	143,316	145,441	145,084	140,031	135,343	574,906		565,899		495,709
Provision/(reversal) for loan losses	(5,000)	(2,000)	0	0	0	(1,500)	0	(3,000)	(7,000)		(4,500)		(2,500)
Net-interest income after reversal for loan losses	146,211	149,000	143,379	143,316	145,441	146,584	140,031	138,343	581,906		570,399		498,209
Non-interest income	8,648	10,388	12,794	12,921	10,795	7,835	7,767	5,310	44,751	[1]	31,707	[1]	36,297	[1]
Non-interest expense	71,192	65,580	69,546	70,970	74,395	65,964	63,088	60,971	277,288		264,419		236,199
Income before income tax expense	83,667	93,808	86,627	85,267	81,841	88,455	84,710	82,682
Total income tax expense, amount	16,290	20,973	14,383	18,588	17,193	18,698	11,046	18,866	70,234		65,802		122,265
Net income	$ 67,377	$ 72,835	$ 72,244	$ 66,679	$ 64,648	$ 69,757	$ 73,664	$ 63,816	$ 279,135		$ 271,885		$ 176,042
Basic (in dollars per share)	$ 0.85	$ 0.91	$ 0.90	$ 0.83	$ 0.80	$ 0.86	$ 0.91	$ 0.79	$ 3.49		$ 3.35		$ 2.19
Diluted (in dollars per share)	$ 0.84	$ 0.91	$ 0.90	$ 0.83	$ 0.80	$ 0.85	$ 0.90	$ 0.78	$ 3.48		$ 3.33		$ 2.17

[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 consolidated prior period amounts to conform to the periods presentation.