Condensed Financial Statements of United Community Banks, Inc. (Holding Company Only) - Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities:
Net income	$ 269,801	$ 164,089	$ 185,721
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	6,554	7,887	9,360
Changes in assets and liabilities:
Other assets	53,416	(20,139)	(45,789)
Net cash provided by operating activities	359,320	158,681	153,933
Investing activities:
Net cash (paid) received for acquisition	103,065	195,699	(19,545)
Purchases of premises and equipment	(26,483)	(18,462)	(20,944)
Proceeds from sale of premises and equipment	4,247	903	6,595
Other investing inflows	767	5,241	1,916
Other investing outflows	(610)	0	0
Net cash (used in) provided by investing activities	(1,806,403)	(1,580,563)	163,218
Financing activities:
Proceeds from issuance of Series I preferred stock, net of issuance costs	0	96,422	0
Cash paid for shares withheld to cover payroll taxes related to equity instruments	(3,182)	(3,119)	(1,686)
Proceeds from issuance of common stock for dividend reinvestment and employee benefit plans	506	1,317	2,193
Proceeds from exercise of options and warrants	231	0	212
Repurchase of common stock	(15,101)	(20,782)	(13,020)
Cash dividends on preferred stock	(6,876)	(3,533)	0
Cash dividends on common stock	(66,914)	(58,912)	(53,044)
Net cash (used in) provided by financing activities	2,156,974	2,515,295	(129,210)
Net change in cash and cash equivalents	709,891	1,093,413	187,941
Cash and cash equivalents at beginning of year	1,608,619	515,206	327,265
Cash and cash equivalents at end of year	2,318,510	1,608,619	515,206
Holding Company
Operating activities:
Net income	269,801	164,089	185,721
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of the subsidiaries	(61,065)	(27,419)	(186,708)
Stock-based compensation	6,554	7,887	9,360
Changes in assets and liabilities:
Other assets	(7,800)	(3,662)	(3,022)
Other liabilities	6,353	5,261	2,080
Net cash provided by operating activities	213,843	146,156	7,431
Investing activities:
Net cash (paid) received for acquisition	(47,785)	3,397	(52,093)
Purchases of premises and equipment	(30)	0	0
Purchases of debt securities available-for-sale and equity securities	(1,500)	(2,750)	(3,000)
Proceeds from sales and maturities of debt securities available-for-sale and equity securities	1,253	0	83
Proceeds from sale of premises and equipment	728	0	0
Other investing inflows	132	0	0
Other investing outflows	(600)	0	0
Net cash (used in) provided by investing activities	(47,802)	647	(55,010)
Financing activities:
Repayment of long-term debt	(65,632)	0	(250)
Proceeds from issuance of long-term debt, net of issuance costs	0	98,552	0
Proceeds from issuance of Series I preferred stock, net of issuance costs	0	96,422	0
Cash paid for shares withheld to cover payroll taxes related to equity instruments	(3,182)	(3,119)	(1,686)
Proceeds from issuance of common stock for dividend reinvestment and employee benefit plans	506	1,317	2,193
Proceeds from exercise of options and warrants	231	0	212
Repurchase of common stock	(15,101)	(20,782)	(13,020)
Cash dividends on preferred stock	6,876	3,533	0
Cash dividends on common stock	(66,914)	(58,912)	(53,044)
Net cash (used in) provided by financing activities	(156,968)	109,945	(65,595)
Net change in cash and cash equivalents	9,073	256,748	(113,174)
Cash and cash equivalents at beginning of year	289,243	32,495	145,669
Cash and cash equivalents at end of year	$ 298,316	$ 289,243	$ 32,495