Major classes of assets and liabilities held for sale (Details 4) - USD ($) $ in Thousands		Mar. 31, 2017		Dec. 31, 2016		Mar. 31, 2016
Current assets:
Total current assets held for sale		$ 7,290		$ 14,391		$ 99,544
Noncurrent assets:
Total noncurrent assets held for sale		95,719		196,664		485,885
Current liabilities:
Current liabilities held for sale		2,394		9,924		117,777
Deferred credits and other liabilities:
Noncurrent liabilities held for sale		0		0		62,625
Exploration and production [Member] | Discontinued operations, held-for-sale or disposed of by sale [Member]
Current assets:
Receivables, net		266		355		3,619
Inventories		0		0		1,308
Income taxes receivable		0		0		50,478
Prepayments and other current assets		0		0		2,348
Total current assets held for sale		266		355		57,753
Noncurrent assets:
Investments		0		0		37
Net property, plant and equipment		4,515		5,507		9,363
Deferred income taxes		91,098		91,098		82,994
Other		161		161		161
Less allowance for impairment of assets held for sale		0		938		(1,374)
Total noncurrent assets held for sale		95,774		95,828		93,929
Total assets held for sale		96,040		96,183		151,682
Current liabilities:
Accounts payable		67		141		7,963
Taxes payable		4,732	[1]	19	[1]	35
Accrued compensation		0		0		761
Other accrued liabilities		2,311		2,358		4,791
Current liabilities held for sale		7,110		2,518		13,550
Deferred credits and other liabilities:
Total liabilities held for sale		7,110		2,518		13,550
Refining [Member] | Discontinued operations, held-for-sale or disposed of by sale [Member]
Current assets:
Cash and cash equivalents		0		0		365
Receivables, net		0		0		11,169
Inventories		0		0		17,056
Income taxes receivable		11,756		13,987		7,077
Prepayments and other current assets		0		0		6,124
Total current assets held for sale		11,756		13,987		41,791
Noncurrent assets:
Net property, plant and equipment		0		0		407,247
Other		0		0		8,846
Total noncurrent assets held for sale		0		0		416,093
Total assets held for sale		11,756		13,987		457,884
Current liabilities:
Short-term borrowings		0		0		61,525
Long-term debt due within one year		0		0		6,375
Accounts payable		16		7,425		27,454
Taxes payable		0		0		1,001
Accrued compensation		0		0		717
Other accrued liabilities		0		0		7,155
Current liabilities held for sale		16		7,425		104,227
Deferred credits and other liabilities:
Long-term debt		0		0		62,625
Deferred income taxes (a)	[2]	55		14		24,137
Noncurrent liabilities held for sale		55		14		86,762
Total liabilities held for sale		$ 71		$ 7,439		$ 190,989

[1] On the Company's Consolidated Balance Sheets, these amounts were reclassified to prepayments and other current assets and are reflectedin current assets held for sale.

[2] On the Company's Consolidated Balance Sheets, these amounts were reclassified to noncurrent deferred income tax assets and are reflected in noncurrent assets held for sale.