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, 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
Quarterly Financial Information Disclosure [Abstract]
Total interest income	$ 57,223	$ 55,351	$ 53,084	$ 50,475	$ 50,211	$ 46,338	$ 43,691	$ 41,084	$ 216,133	$ 181,324	$ 161,241
Total interest expense	17,062	15,389	14,139	12,328	10,403	9,319	8,590	7,943	58,918	36,255	31,096
Net interest income	40,161	39,962	38,945	38,147	39,808	37,019	35,101	33,141	157,215	145,069	130,145
Provision for loan losses	1,100	1,100	1,100	17,800	2,000	1,450	1,450	1,100	21,100	6,000	38,700
Total other income, net of securities gains	1,515	1,429	1,388	1,407	2,024	1,756	1,422	1,406
Net securities gains								1,596
Other expense	18,266	18,287	17,108	17,059	16,566	18,641	25,303	18,249
Income before income taxes	22,310	22,004	22,125	4,695	23,266	18,684	9,770	16,794	71,134	68,514	42,858
Income tax expense	3,638	2,102	4,598	444	12,686	5,607	2,087	4,914	10,782	25,294	11,776
Net income	$ 18,672	$ 19,902	$ 17,527	$ 4,251	$ 10,580	$ 13,077	$ 7,683	$ 11,880	$ 60,352	$ 43,220	$ 31,082
Earnings per share:
Basic (in Dollars per share)	$ 0.58	$ 0.62	$ 0.54	$ 0.13	$ 0.33	$ 0.41	$ 0.24	$ 0.37	$ 1.87	$ 1.35	$ 1.02
Diluted (in Dollars per share)	$ 0.58	$ 0.61	$ 0.54	$ 0.13	$ 0.33	$ 0.41	$ 0.24	$ 0.37	$ 1.86	$ 1.34	$ 1.01