EARNINGS PER SHARE - Computation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
EARNINGS PER SHARE.
Net income	$ 8,977	$ 13,061	$ 10,656	$ 9,348	$ 14,208	$ 13,903	$ 10,653	$ 12,927	$ 42,042	$ 51,691	$ 39,227
Dividends paid on and earnings allocated to participating securities									(872)	(1,096)	(853)
Income attributable to common stock									$ 41,170	$ 50,595	$ 38,374
Weighted average common shares outstanding, including participating securities									19,903	19,952	19,875
Weighted average participating securities (in shares)									(409)	(424)	(434)
Weighted average common shares outstanding									19,494	19,528	19,441
Basic earnings per common share (in dollars per share)	$ 0.45	$ 0.66	$ 0.54	$ 0.47	$ 0.71	$ 0.70	$ 0.53	$ 0.65	$ 2.11	$ 2.59	$ 1.97
Income attributable to common stock									$ 41,170	$ 50,595	$ 38,374
Weighted average common shares outstanding									19,494	19,528	19,441
Incremental shares from assumed conversions of options and restricted stock units									55	31	27
Weighted average common and equivalent shares outstanding (in shares)									19,549	19,559	19,468
Diluted earnings per common share (in dollars per share)	$ 0.45	$ 0.66	$ 0.54	$ 0.47	$ 0.71	$ 0.70	$ 0.53	$ 0.65	$ 2.11	$ 2.59	$ 1.97