LEASES - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Operating leases:
Operating leases - right of use assets	$ 25,891	$ 28,154
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating leases - right of use assets	Operating leases - right of use assets
Current operating lease obligations	$ 7,127	$ 6,838
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current operating lease obligations	Current operating lease obligations
Long-term operating lease obligations	$ 19,145	$ 21,690
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term operating lease obligations	Long-term operating lease obligations
Total operating lease liabilities	$ 26,272	$ 28,528
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OperatingLeaseLiabilityCurrent us-gaap:OperatingLeaseLiabilityNoncurrent	us-gaap:OperatingLeaseLiabilityCurrent us-gaap:OperatingLeaseLiabilityNoncurrent
Finance leases:
Property and equipment, at cost	$ 86,114	$ 86,281
Accumulated amortization	(28,595)	(22,991)
Property and equipment, net	57,519	63,290
Current finance lease obligations	$ 11,852	$ 11,655
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current finance lease obligations	Current finance lease obligations
Long-term finance lease obligations	$ 48,397	$ 54,482
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term finance lease obligations	Long-term finance lease obligations
Total lease obligations	$ 60,249	$ 66,137
Weighted average remaining lease term:
Operating leases	54 months	60 months
Finance leases	37 months	43 months
Weighted average discount rate:
Operating leases	4.53%	4.59%
Finance leases	3.73%	3.73%