LEASES - Schedule of future maturities of lease liabilities (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Finance
Remainder of 2019	$ 8,492
2020	20,224
2021	6,563
2022	151
2023	130
Thereafter	13
Total minimum lease payments	35,573
Less amount representing interest	1,782
Present value of minimum lease payments	33,791
Operating
Remainder of 2019	12,235
2020	23,921
2021	23,134
2022	13,341
2023	6,504
Thereafter	22,239
Total minimum lease payments	101,374
Less amount representing interest	17,110
Present value of minimum lease payments	84,264
Mining equipment
Finance
Remainder of 2019	1,849
2020	3,699
2021	2,157
2022	0
2023	0
Thereafter	0
Total minimum lease payments	7,705
Operating
Remainder of 2019	774
2020	627
2021	0
2022	0
2023	0
Thereafter	0
Total minimum lease payments	$ 1,401