EARNINGS PER SHARE - Computation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
EARNINGS PER SHARE.
Net income	$ 13,061	$ 13,903	$ 33,065	$ 37,483
Dividends paid on and earnings allocated to participating securities	(276)	(294)	(689)	(797)
Income attributable to common stock	$ 12,785	$ 13,609	$ 32,376	$ 36,686
Weighted average common shares outstanding, including participating securities	19,896	19,958	19,901	19,950
Weighted average participating securities (in shares)	(423)	(422)	(415)	(425)
Weighted average common shares outstanding	19,473	19,536	19,486	19,525
Basic earnings per common share (in dollars per share)	$ 0.66	$ 0.70	$ 1.66	$ 1.88
Income attributable to common stock	$ 12,785	$ 13,609	$ 32,376	$ 36,686
Weighted average common shares outstanding	19,473	19,536	19,486	19,525
Incremental shares from assumed conversions of options and restricted stock units	41	32	36	27
Weighted average common and equivalent shares outstanding (in shares)	19,514	19,568	19,522	19,552
Diluted earnings per common share (in dollars per share)	$ 0.66	$ 0.70	$ 1.66	$ 1.88