Shareholders' Equity - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2014
Equity [Abstract]
Cash dividend payments, per share	$ 0.14	$ 0.11	$ 0.07
Home Savings retained earnings distributed	$ 0
Dividend received by United Community from Home Savings	15,000,000
Reclassification of net gains or (losses) included in accumulated other comprehensive income	566,000	$ 604,000	$ 142,000
Effect of disproportionate tax on accumulated other comprehensive income (loss)				$ (16,600,000)
Home Savings established a liquidation account, totaling	$ 141,400,000