EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
EARNINGS PER SHARE
Weighted-average anti-dilutive stock options outstanding (in shares)	200,000	500,000	100,000	700,000
Basic earnings per share
Net Income (Loss) Attributable to Parent	$ 45,336	$ 42,809	$ 146,130	$ 118,191
Income attributable to unvested stock-based compensation awards	(110)	(147)	(340)	(432)
Income available to common shareholders	$ 45,226	$ 42,662	$ 145,790	$ 117,759
Weighted-average common shares outstanding - basic (in shares)	54,025,000	53,650,000	53,960,000	52,727,000
Basic earnings per share (in dollars per share)	$ 0.84	$ 0.80	$ 2.70	$ 2.23
Diluted earnings per share
Net Income (Loss) Attributable to Parent	$ 45,336	$ 42,809	$ 146,130	$ 118,191
Income attributable to unvested stock-based compensation awards	(110)	(147)	(340)	(432)
Income available to common shareholders	$ 45,226	$ 42,662	$ 145,790	$ 117,759
Weighted-average common shares outstanding (in shares)	54,025,000	53,650,000	53,960,000	52,727,000
Assumed exercise of stock options (in shares)	385,000	324,000	431,000	356,000
Weighted-average common shares outstanding - diluted (in shares)	54,410,000	53,974,000	54,391,000	53,083,000
Diluted earnings per share (in dollars per share)	$ 0.83	$ 0.79	$ 2.68	$ 2.22
Cash dividends declared per share (in dollars per share)	$ 0.43	$ 0.42	$ 1.27	$ 1.24
Stock Repurchase Program
Number of common shares authorized to be repurchased (in shares)					2,680,000	2,600,000
Number of common shares repurchased (in shares)			0		0