EARNINGS PER SHARE - Earnings Per Share Computations (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 PER SHARE
Net income	$ 24,592	$ 22,776	$ 19,670	$ 17,299	$ 22,198	$ 21,454	$ 21,713	$ 21,682	$ 84,337	$ 87,047	$ 80,411
Weighted-average common shares outstanding									25,469,242	25,588,404	25,288,533
Basic earnings per common share	$ 0.97	$ 0.89	$ 0.77	$ 0.68	$ 0.86	$ 0.84	$ 0.85	$ 0.85	$ 3.31	$ 3.40	$ 3.18
Diluted earnings per common share:
Net income	$ 24,592	$ 22,776	$ 19,670	$ 17,299	$ 22,198	$ 21,454	$ 21,713	$ 21,682	$ 84,337	$ 87,047	$ 80,411
BASIC WEIGHTED AVERAGE COMMON SHARES									25,469,242	25,588,404	25,288,533
Add: Dilutive effect of assumed exercise of warrant											225,831
Add: Dilutive effect of assumed exercises of stock options and awards									104,699	170,489	213,467
Average shares and dilutive potential common shares									25,573,941	25,758,893	25,727,831
Diluted earnings per common share	$ 0.97	$ 0.89	$ 0.77	$ 0.67	$ 0.86	$ 0.83	$ 0.85	$ 0.84	$ 3.30	$ 3.38	$ 3.13