Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 143,157	$ 139,681	$ 133,477
Asphalt oil	39,269	54,741	40,781
Materials and supplies	25,696	23,611	23,563
Merchandise for resale	23,902	22,552	15,954
Natural gas in storage (current)	32,164	22,117	29,084
Other	21,869	24,607	27,434
Total	286,057	287,309	270,293
Natural gas in storage noncurrent	$ 48,200	$ 48,500	$ 47,800

Aggregated amount of aggregates held for resale. This amount is net of valuation reserves and adjustments.

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- Definition

Aggregated amount of asphalt oil inventory. This amount is net of valuation reserves and adjustments.

+ References

No definition available.

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- Definition

Carrying amount as of the balance sheet date of natural gas in storage, which is a mixture of gases (liquefied or otherwise), used for fuel and manufacturing purposes, which is ready for sale.

+ References

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- Definition

Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer.

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Carrying amount as of the balance sheet date of natural gas stored underground in depleted gas reservoirs, aquifers, or salt caverns to meet future seasonal and peak load demands and also as insurance against unforeseen supply disruptions, and deemed to be a noncurrent asset because it is not expected to be used within 12 months or in the normal operating cycle.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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- Definition

Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

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Amount, after of valuation reserves and allowances, of inventory, classified as other, expected to be sold, or consumed within one year or operating cycle, if longer.

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