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, 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
Quarterly Financial Information Disclosure [Abstract]
Total interest income	$ 68,008	$ 70,389	$ 67,878	$ 65,209	$ 57,223	$ 55,351	$ 53,084	$ 50,475	$ 271,484	$ 216,133	$ 181,324
Total interest expense	20,577	21,983	22,348	20,257	17,062	15,389	14,139	12,328	85,165	58,918	36,255
Net interest income	47,431	48,406	45,530	44,952	40,161	39,962	38,945	38,147	186,319	157,215	145,069
Provision for loan losses	500	2,000	1,100	4,500	1,100	1,100	1,100	17,800	8,100	21,100	6,000
Total other income, net of securities gains	2,246	2,109	1,942	1,738	1,515	1,429	1,388	1,407
Other expense	22,197	20,379	21,590	28,062	18,266	18,287	17,108	17,059
Income before income taxes	26,980	28,136	24,782	14,128	22,310	22,004	22,125	4,695	94,026	71,134	68,514
Income tax expense	6,197	6,440	5,501	2,493	3,638	2,102	4,598	444	20,631	10,782	25,294
Net income	$ 20,783	$ 21,696	$ 19,281	$ 11,635	$ 18,672	$ 19,902	$ 17,527	$ 4,251	$ 73,395	$ 60,352	$ 43,220
Earnings per share:
Basic (in Dollars per share)	$ 0.59	$ 0.60	$ 0.55	$ 0.33	$ 0.58	$ 0.62	$ 0.54	$ 0.13	$ 2.08	$ 1.87	$ 1.35
Diluted (in Dollars per share)	$ 0.59	$ 0.60	$ 0.54	$ 0.33	$ 0.58	$ 0.61	$ 0.54	$ 0.13	$ 2.07	$ 1.86	$ 1.34