Condensed Financial Statements of Unity Bancorp, Inc. (Parent Company Only) - Condensed Statements of Income (Details) - USD ($) $ 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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Dividend from Bank	$ 19,312	$ 19,055	$ 18,781	$ 18,500	$ 18,060	$ 17,194	$ 16,369	$ 15,640	$ 15,044	$ 14,195	$ 13,477	$ 12,594	$ 75,648	$ 67,263	$ 55,310
Gain on sales of securities													373	(199)	62
Other income													1,346	1,207	1,108
Total noninterest income	2,398	2,710	2,411	2,020	1,954	2,479	2,312	2,286	2,037	2,008	2,021	2,204	9,539	9,031	8,270
Interest expenses	4,549	4,651	4,571	4,284	3,896	3,627	3,225	2,768	2,544	2,378	2,327	2,204	18,055	13,516	9,453
Market value (appreciation) write-downs on equity securities													(321)	195
Other expenses													1,877	1,782	1,883
Benefit (provision) for income taxes	1,820	1,676	1,646	1,520	1,547	1,255	1,351	1,235	3,908	2,014	1,906	1,712
Net income	$ 6,120	$ 5,959	$ 5,834	$ 5,740	$ 5,803	$ 5,490	$ 5,397	$ 5,229	$ 2,500	$ 3,757	$ 3,444	$ 3,192	23,653	21,919	12,893
Parent Company Only
Condensed Financial Statements, Captions [Line Items]
Dividend from Bank													3,300	2,890	2,452
Gain on sales of securities													17	0	0
Other income													454	425	413
Total noninterest income													3,771	3,315	2,865
Interest expenses													366	251	251
Market value (appreciation) write-downs on equity securities													(293)	171	0
Other expenses													251	261	251
Total expenses													324	683	502
Income before provision for income taxes and equity in undistributed net income of subsidiary													3,447	2,632	2,363
Benefit (provision) for income taxes													78	(14)	(15)
Income before equity in undistributed net income of subsidiary													3,369	2,646	2,378
Equity in undistributed net income of subsidiary													20,284	19,273	10,515
Net income													$ 23,653	$ 21,919	$ 12,893