LEASES - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating leases:
Operating leases - right of use assets	$ 28,154	$ 11,775
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	$ 6,838	$ 6,050
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current operating lease obligations	Current operating lease obligations
Long-term operating lease obligations	$ 21,690	$ 5,812
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term operating lease obligations	Long-term operating lease obligations
Total operating lease liabilities	$ 28,528	$ 11,862
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	$ 86,281	$ 120,236
Accumulated amortization	(22,991)	(30,990)
Property and equipment, net	63,290	89,246
Current finance lease obligations	$ 11,655	$ 30,779
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current finance lease obligations	Current finance lease obligations
Long-term finance lease obligations	$ 54,482	$ 58,397
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term finance lease obligations	Long-term finance lease obligations
Total lease obligations	$ 66,137	$ 89,176
Finance Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:FinanceLeaseLiabilityCurrent us-gaap:FinanceLeaseLiabilityNoncurrent	us-gaap:FinanceLeaseLiabilityCurrent us-gaap:FinanceLeaseLiabilityNoncurrent
Weighted average remaining lease term:
Operating leases	60 months	45 months
Finance leases	43 months	44 months
Weighted average discount rate:
Operating leases	4.59%	4.03%
Finance leases	3.73%	3.34%