Leases (Breakdown of Lease Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Leases
Operating lease cost	$ 16,927	$ 17,878
Amortization of leased assets	9,268	7,510
Interest on lease liabilities	915	800
Short-term lease cost	9,799	9,090
Sublease income	(429)	(559)
Lease expense	$ 36,480	$ 34,719

Amount of interest expense on finance lease liability.

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

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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.

+ References

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Amount of short-term lease cost, excluding expense for lease with term of one month or less.

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- Definition

Amount of sublease income excluding finance and operating lease expense.

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