EARNINGS PER SHARE - Computation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
EARNINGS PER SHARE.
Net income	$ 13,903	$ 6,547	$ 37,483	$ 25,363
Dividends paid on and earnings allocated to participating securities	(294)	(145)	(797)	(550)
Income attributable to common stock	$ 13,609	$ 6,402	$ 36,686	$ 24,813
Weighted average common shares outstanding, including participating securities	19,958	19,890	19,950	19,869
Weighted average participating securities (in shares)	(422)	(438)	(425)	(435)
Weighted average common shares outstanding	19,536	19,452	19,525	19,434
Basic earnings per common share (in dollars per share)	$ 0.70	$ 0.33	$ 1.88	$ 1.28
Income attributable to common stock	$ 13,609	$ 6,402	$ 36,686	$ 24,813
Weighted average common shares outstanding	19,536	19,452	19,525	19,434
Incremental shares from assumed conversions of options and restricted stock units	32	33	27	27
Weighted average common and equivalent shares outstanding (in shares)	19,568	19,485	19,552	19,461
Diluted earnings per common share (in dollars per share)	$ 0.70	$ 0.33	$ 1.88	$ 1.28