Discontinued Operations and Assets Held for Sale (Major Categories of Assets and Liabilities Reflected as Held for Sale) (Details) $ in Thousands	1 Months Ended
	Nov. 05, 2020 airplane	Sep. 30, 2020 USD ($) airplane	Jun. 30, 2020 airplane	Dec. 31, 2019 USD ($)
Current liabilities
Total current liabilities associated with assets held for sale		$ 14,677		$ 13,298
Number of airplanes held for sale (in airplanes) | airplane		2	2
Subsequent Event
Current liabilities
Number of airplanes sold (in airplanes) | airplane	1
Discontinued Operations, Held-for-sale or Disposed of by Sale | Brunei Exploration And Production Operations
Current assets
Cash		$ 29,420		25,185
Accounts receivable		425		4,834
Inventories		406		406
Prepaid expenses and other		831		1,882
Property, plant, and equipment, net		68,393		82,116
Deferred income taxes and other assets		9,441		9,441
Total current assets associated with assets held for sale		108,916		123,864
Current liabilities
Accounts payable		5,481		3,702
Current maturities of long-term debt (finance lease)		728		705
Taxes payable		1,510		1,411
Long-term debt (finance lease)		6,702		7,240
Asset retirement obligation		256		240
Total current liabilities associated with assets held for sale		$ 14,677		$ 13,298