COMMITMENTS AND CONTINGENCIES - Leases: Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Operating lease expense	$ 9,697	$ 7,701	$ 27,203	$ 23,138
Amortization of finance lease assets	154	127	408	346
Interest on finance lease liabilities	7	11	24	33
Total lease expense	$ 9,858	$ 7,839	$ 27,635	$ 23,517

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Amount of interest expense on finance lease liability.

+ References

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Amount of amortization expense attributable to right-of-use asset from finance lease.

+ References

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- Definition

Amount of lease cost recognized by lessee for lease contract.

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Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability.

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