NET EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings (Numerator) [Abstract]
Net earnings	$ 22,162	$ 21,568	$ 21,125	$ 19,768	$ 20,383	$ 20,676	$ 19,829	$ 18,783	$ 84,623	$ 79,671	$ 78,573
Number of Shares (Denominator) [Abstract]
Weighted average common shares - basic (in shares)									32,176,000	32,136,000	32,093,000
Effect of dilutive securities - stock options, restricted stock, and performance shares (in shares)									327,000	369,000	352,000
Weighted average common shares - diluted (in shares)									32,503,000	32,505,000	32,445,000
Per Share Amount [Abstract]
Net earnings per share - basic (in dollars per share)	$ 0.69	$ 0.67	$ 0.66	$ 0.62	$ 0.64	$ 0.64	$ 0.62	$ 0.58	$ 2.63	$ 2.48	$ 2.45
Net earnings per share - diluted (in dollars per share)	$ 0.68	$ 0.66	$ 0.65	$ 0.61	$ 0.63	$ 0.64	$ 0.61	$ 0.58	$ 2.60	$ 2.45	$ 2.42
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding, excluded from diluted earnings per share calculation (in shares)									204,672	12,250	188,470