EMPLOYEE BENEFITS - Supplemental Executive Retirement Plans and Long Term Incentive Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation expense	$ 900	$ 1,200	$ (400)
Restructuring	0	1,646	7,828
Holding Company SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit obligation	7,500	7,500
Net periodic benefit cost	$ 600	$ 800	$ 0
Benefit obligation, discount rate	2.45%	3.10%	4.15%
Pacific Northwest SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit obligation	$ 3,200	$ 3,100
Net periodic benefit cost	$ 100	$ 200	$ 200
Benefit obligation, discount rate	2.45%	3.10%	4.18%
KLS LTIP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit obligation	$ 6,100	$ 7,900
Benefit obligation, discount rate	2.45%	3.10%	4.10%
Compensation expense	$ 400	$ 700	$ 1,600
Restructuring			$ 800