EARNINGS PER SHARE - Computation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
EARNINGS PER SHARE.
Net income	$ 10,653	$ 6,743	$ 23,580	$ 18,816
Dividends paid on and earnings allocated to participating securities	(226)	(148)	(503)	(405)
Income attributable to common stock	$ 10,427	$ 6,595	$ 23,077	$ 18,411
Weighted average common shares outstanding, including participating securities	19,965	19,884	19,946	19,859
Weighted average participating securities (in shares)	(428)	(445)	(427)	(433)
Weighted average common shares outstanding	19,537	19,439	19,519	19,426
Basic earnings per common share (in dollars per share)	$ 0.53	$ 0.34	$ 1.18	$ 0.95
Income attributable to common stock	$ 10,427	$ 6,595	$ 23,077	$ 18,411
Weighted average common shares outstanding	19,537	19,439	19,519	19,426
Incremental shares from assumed conversions of options and restricted stock units	28	29	26	27
Weighted average common and equivalent shares outstanding (in shares)	19,565	19,468	19,545	19,453
Diluted earnings per common share (in dollars per share)	$ 0.53	$ 0.34	$ 1.18	$ 0.95