Leases (Breakdown of Lease Expense) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Leases
Operating lease cost	$ 4,392	$ 3,969	$ 8,992	$ 8,470
Amortization of leased assets	2,815	2,195	5,403	4,309
Interest on lease liabilities	205	229	426	462
Short-term lease cost	1,922	2,151	4,583	5,031
Sublease income	(15)	(148)	(30)	(296)
Lease expense	$ 9,319	$ 8,396	$ 19,374	$ 17,976

Amount of interest expense on finance lease liability.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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- Definition

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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971

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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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