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Inventories and natural gas in storage (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Inventory Disclosure [Abstract]
Aggregates held for resale	$ 123,457	$ 108,161	$ 112,129
Asphalt oil	79,422	42,135	76,525
Materials and supplies	22,594	54,282	58,089
Merchandise for resale	16,140	24,420	25,507
Refined products	16,065	0	0
Natural gas in storage (current)	11,310	19,302	10,903
Crude oil	8,101	5,045	0
Other	37,316	36,065	35,420
Total	314,405	289,410	318,573
Natural gas in storage noncurrent	$ 49,300	$ 49,300	$ 47,400

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- Definition

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

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

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Carrying amount as of the balance sheet date of natural gas in storage, which largely represents the cost of gas required to maintain pressure levels for normal operating purposes, and deemed to be noncurrent asset.

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The aggregate carrying amount as of the balance sheet date of unrefined petroleum and the liquid hydrocarbon components recovered from natural gas.

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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.

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Carrying amount as of the balance sheet date of finished goods inventories for petroleum products, crude oil, petrochemical products, and other oil and gas inventories.

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

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Carrying amount, net of valuation reserves and allowances, as of the balance sheet date of inventories not otherwise specified in the taxonomy.

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