Merger - Additional Information (Detail) - UCB and United Community Bank [Member] $ / shares in Units, $ in Millions		3 Months Ended
	Mar. 11, 2018 Bank $ / shares shares	Mar. 31, 2018	Dec. 31, 2017 USD ($)
Business Combinations [Line Items]
Date of acquisition agreement		Mar. 11, 2018
Number of banking offices acquired | Bank	8
Total consolidated assets | $			$ 546
Total loans | $			296
Total deposits | $			$ 462
Per share common stock	$ 1.027
Per share cash consideration	$ 2.54
Stock options outstanding | shares	212,563
Share price per share	$ 26.22
Aggregate cash consideration to be paid	$ 13,600,000