Discontinued Operations and Assets Held for Sale (Major Categories of Assets and Liabilities Reflected as Held for Sale) (Details) $ in Thousands	Jun. 30, 2020 USD ($) airplane	Dec. 31, 2019 USD ($)
Discontinued Operations and Disposal Groups [Abstract]
Number of airplanes held for sale (in airplanes) | airplane	2
Current liabilities
Total current liabilities associated with assets held for sale	$ 13,711	$ 13,298
Discontinued Operations, Held-for-sale or Disposed of by Sale | Brunei Exploration And Production Operations
Current assets
Cash	30,898	25,185
Accounts receivable	425	4,834
Inventories	406	406
Prepaid expenses and other	814	1,882
Property, plant, and equipment, net	82,353	82,116
Deferred income taxes and other assets	9,441	9,441
Total current assets associated with assets held for sale	124,337	123,864
Current liabilities
Accounts payable	4,342	3,702
Current maturities of long-term debt (finance lease)	720	705
Taxes payable	1,510	1,411
Long-term debt (finance lease)	6,889	7,240
Asset retirement obligation	250	240
Total current liabilities associated with assets held for sale	$ 13,711	$ 13,298