Quarterly Financial Information of ConnectOne Bancorp, Inc. (Unaudited) (Details) - Schedule of Quarterly Financial Information - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total interest income	$ 75,588	$ 77,221	$ 78,677	$ 76,714	$ 68,008	$ 70,389	$ 67,878	$ 65,209	$ 308,200	$ 271,484	$ 216,133
Total interest expense	14,217	16,672	17,887	21,433	20,577	21,983	22,348	20,257	70,209	85,165	58,918
Net interest income	61,371	60,549	60,790	55,281	47,431	48,406	45,530	44,952	237,991	186,319	157,215
Provision for loan losses	5,000	5,000	15,000	16,000	500	2,000	1,100	4,500	41,000	8,100	21,100
Total other income, net of securities gains	3,442	3,483	4,621	2,854	2,246	2,109	1,942	1,738
Other expenses	26,402	26,478	33,063	35,058	22,197	20,379	21,590	28,062
Income before income taxes	33,411	32,554	17,348	7,077	26,980	28,136	24,782	14,128	90,390	94,026	71,134
Income tax expense	7,770	7,768	2,516	1,047	6,197	6,440	5,501	2,493	19,101	20,631	10,782
Net income	$ 25,641	$ 24,786	$ 14,832	$ 6,030	$ 20,783	$ 21,696	$ 19,281	$ 11,635	$ 71,289	$ 73,395	$ 60,352
Earnings per share:
Basic (in Dollars per share)	$ 0.64	$ 0.62	$ 0.37	$ 0.15	$ 0.59	$ 0.60	$ 0.55	$ 0.33	$ 1.80	$ 2.08	$ 1.87
Diluted (in Dollars per share)	$ 0.64	$ 0.62	$ 0.37	$ 0.15	$ 0.59	$ 0.60	$ 0.54	$ 0.33	$ 1.79	$ 2.07	$ 1.86