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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Dividend from Bank	$ 18,060	$ 17,194	$ 16,369	$ 15,640	$ 15,044	$ 14,195	$ 13,477	$ 12,594	$ 12,280	$ 12,081	$ 11,487	$ 11,176	$ 67,263	$ 55,310	$ 47,024
Gain on repurchase of subordinated debt													0	0	2,264
Gains on sales of securities													(199)	62	424
Other income													1,207	1,108	985
Total noninterest income	1,954	2,479	2,312	2,286	2,037	2,008	2,021	2,204	2,373	2,173	2,234	4,280	9,031	8,270	11,060
Interest expenses	3,896	3,627	3,225	2,768	2,544	2,378	2,327	2,204	2,225	2,208	2,145	2,189	13,516	9,453	8,767
Other expenses													1,782	1,883	1,842
Benefit (provision) for income taxes	1,547	1,255	1,351	1,235	3,908	2,014	1,906	1,712	1,765	1,613	1,624	2,255
Net income	$ 5,803	$ 5,490	$ 5,397	$ 5,229	$ 2,500	$ 3,757	$ 3,444	$ 3,192	$ 3,160	$ 3,020	$ 2,824	$ 4,205	21,919	12,893	13,209
Parent Company Only
Condensed Financial Statements, Captions [Line Items]
Dividend from Bank													2,890	2,452	6,598
Gain on repurchase of subordinated debt													0	0	994
Gains on sales of securities													0	0	177
Other income													425	413	692
Total noninterest income													3,315	2,865	8,461
Interest expenses													251	251	265
Market value write-downs on equity securities													171	0	0
Other expenses													261	251	245
Total expenses													683	502	510
Income before provision for income taxes and equity in undistributed net income of subsidiary													2,632	2,363	7,951
Benefit (provision) for income taxes													(14)	(15)	550
Income before equity in undistributed net income of subsidiary													2,646	2,378	7,401
Equity in undistributed net income of subsidiary													19,273	10,515	5,808
Net income													$ 21,919	$ 12,893	$ 13,209