STOCK-BASED COMPENSATION - Summary of restricted stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Non-performance based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares underlying restricted stock	191,896	161,443	200,660	181,773
Weighted-average grant date fair value per share	$ 28.33	$ 28.20	$ 27.54	$ 27.05
Aggregate fair value (in thousands)	$ 3,410
Weighted-average remaining vesting period (years)	2 years 7 months 6 days
Performance-based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares underlying restricted stock	18,000	18,000	24,000	24,000
Weighted-average grant date fair value per share	$ 34.46	$ 34.46	$ 34.46	$ 34.46
Aggregate fair value (in thousands)	$ 320
Weighted-average remaining vesting period (years)	2 years 7 months 6 days