EARNINGS PER SHARE - Computation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
EARNINGS PER SHARE.
Net income	$ 14,208	$ 13,903	$ 10,653	$ 12,927	$ 13,864	$ 6,547	$ 6,743	$ 12,073	$ 51,691	$ 39,227	$ 20,539
Dividends paid on and earnings allocated to participating securities									(1,096)	(853)	(415)
Income attributable to common stock									$ 50,595	$ 38,374	$ 20,124
Weighted average common shares outstanding, including participating securities									19,952	19,875	19,759
Weighted average participating securities (in shares)									(424)	(434)	(404)
Weighted average common shares outstanding									19,528	19,441	19,355
Basic earnings per common share (in dollars per share)	$ 0.71	$ 0.70	$ 0.53	$ 0.65	$ 0.70	$ 0.33	$ 0.34	$ 0.61	$ 2.59	$ 1.97	$ 1.04
Income attributable to common stock									$ 50,595	$ 38,374	$ 20,124
Weighted average common shares outstanding									19,528	19,441	19,355
Incremental shares from assumed conversions of options and restricted stock units									31	27	24
Weighted average common and equivalent shares outstanding (in shares)									19,559	19,468	19,379
Diluted earnings per common share (in dollars per share)	$ 0.71	$ 0.70	$ 0.53	$ 0.65	$ 0.70	$ 0.33	$ 0.34	$ 0.61	$ 2.59	$ 1.97	$ 1.04