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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Quarterly Financial Information [Abstract]
Total interest income	$ 50,211	$ 46,338	$ 43,691	$ 41,084	$ 41,499	$ 41,178	$ 40,038	$ 38,526	$ 181,324	$ 161,241	$ 140,967
Total interest expense	10,403	9,319	8,590	7,943	8,092	8,154	7,644	7,206	36,255	31,096	23,814
Net interest income	39,808	37,019	35,101	33,141	33,407	33,024	32,394	31,320	145,069	130,145	117,153
Provision for loan losses	2,000	1,450	1,450	1,100	25,200	6,750	3,750	3,000	6,000	38,700	12,605
Total other income, net of securities gains	2,024	1,756	1,422	1,406	1,573	1,445	1,467	1,202
Net securities gains				1,596		4,131	103
Other expense	16,566	18,641	25,303	18,249	15,252	14,551	14,352	14,353
Income before income taxes	23,266	18,684	9,770	16,794	(5,472)	17,299	15,862	15,169	68,514	42,858	61,237
Income tax expense	12,686	5,607	2,087	4,914	(3,448)	5,443	5,003	4,778	25,294	11,776	19,926
Net income	$ 10,580	$ 13,077	$ 7,683	$ 11,880	(2,024)	11,856	10,859	10,391	43,220	31,082	41,311
Preferred dividends								22		22	112
Net income available to common stockholders					$ (2,024)	$ 11,856	$ 10,859	$ 10,369	$ 43,220	$ 31,060	$ 41,199
Earnings per share:
Basic (in Dollars per share)	$ 0.33	$ 0.41	$ 0.24	$ 0.37	$ (0.07)	$ 0.39	$ 0.36	$ 0.35	$ 1.35	$ 1.02	$ 1.37
Diluted (in Dollars per share)	$ 0.33	$ 0.41	$ 0.24	$ 0.37	$ (0.07)	$ 0.39	$ 0.36	$ 0.34	$ 1.34	$ 1.01	$ 1.36