EARNINGS PER SHARE - Computation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
EARNINGS PER SHARE.
Net income	$ 10,656	$ 10,653	$ 20,004	$ 23,580
Dividends paid on and earnings allocated to participating securities	(218)	(226)	(413)	(503)
Income attributable to common stock	$ 10,438	$ 10,427	$ 19,591	$ 23,077
Weighted average common shares outstanding, including participating securities	19,861	19,965	19,904	19,946
Weighted average participating securities (in shares)	(409)	(428)	(411)	(427)
Weighted average common shares outstanding	19,452	19,537	19,493	19,519
Basic earnings per common share (in dollars per share)	$ 0.54	$ 0.53	$ 1.01	$ 1.18
Income attributable to common stock	$ 10,438	$ 10,427	$ 19,591	$ 23,077
Weighted average common shares outstanding	19,452	19,537	19,493	19,519
Incremental shares from assumed conversions of options and restricted stock units	36	28	34	26
Weighted average common and equivalent shares outstanding (in shares)	19,488	19,565	19,527	19,545
Diluted earnings per common share (in dollars per share)	$ 0.54	$ 0.53	$ 1.00	$ 1.18