SUMMARY OF ORGANIZATION - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended
	Aug. 22, 2018	May 22, 2018	Feb. 22, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Organization [Line Items]
Assets				$ 2,508,942		$ 2,508,942		$ 1,813,238
Loans, including Loans held for sale				1,700,000		1,700,000
Deposits				2,046,446		2,046,446		1,470,565
Stockholders' equity				288,798	$ 166,980	288,798	$ 166,980	$ 222,468	$ 154,527
Net income				$ 5,162	$ 4,714	$ 14,364	$ 8,202
Dividends on common stock, per share	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.0375	$ 0.15	$ 0.1125
Noncash Merger Related Costs						$ 3,000