Revenue from Contracts with Customers (Balance Sheet) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
ASSETS
Total assets	$ 5,913,935		$ 6,678,715
Accounts receivable	378,036		427,022
Current income taxes	11,395		58,439
Other current assets and prepayments	92,916		74,589
Noncurrent income taxes	54,114		59,909
Other assets	526,937		540,750
Total Liabilities
Total liabilities	5,662,269		6,490,154
Accounts payable and accrued liabilities	1,342,097		1,450,149
Current income taxes	40,018		8,823
Advance billings	224,141		257,766
Liabilities of discontinued operations	10,446		72,808
Deferred taxes on income	230,663		234,643
Other noncurrent liabilities	443,925		519,079
Stockholders’ equity:
Total stockholders’ equity	251,666		188,561	$ 100,833	$ (103,660)
Retained earnings	5,290,761		5,229,584
Accumulated other comprehensive loss	(804,609)		$ (792,173)
ASC 606
Stockholders’ equity:
Retained earnings		$ (9,000)
Prior guidance | ASC 606
ASSETS
Total assets	5,911,188
Accounts receivable	377,484
Current income taxes	11,593
Other current assets and prepayments	92,174
Noncurrent income taxes	54,117
Other assets	525,283
Total Liabilities
Total liabilities	5,671,251
Accounts payable and accrued liabilities	1,339,257
Current income taxes	32,960
Advance billings	237,546
Liabilities of discontinued operations	10,359
Deferred taxes on income	234,365
Other noncurrent liabilities	445,785
Stockholders’ equity:
Total stockholders’ equity	239,256
Retained earnings	5,278,691
Accumulated other comprehensive loss	(804,949)
Total increase (decrease) | ASC 606
ASSETS
Total assets	2,747
Accounts receivable	552
Current income taxes	(198)
Other current assets and prepayments	742
Noncurrent income taxes	(3)
Other assets	1,654
Total Liabilities
Total liabilities	(8,982)
Accounts payable and accrued liabilities	2,840
Current income taxes	7,058
Advance billings	(13,405)
Liabilities of discontinued operations	87
Deferred taxes on income	(3,702)
Other noncurrent liabilities	(1,860)
Stockholders’ equity:
Total stockholders’ equity	12,410
Retained earnings	12,070
Accumulated other comprehensive loss	$ 340