Revenue from Contracts with Customers (Balance Sheet) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
ASSETS
Total assets	$ 6,246,751		$ 6,678,715
Accounts receivable (net of allowance of $13,515 and $14,786, respectively)	408,703		427,022
Current income taxes	39,100		58,439
Other current assets and prepayments	102,104		74,589
Assets of discontinued operations	313,356		334,848
Noncurrent income taxes	54,099		59,909
Other assets	528,945		540,750
Total Liabilities
Total liabilities	6,050,834		6,490,154
Accounts payable and accrued liabilities	1,349,344		1,450,149
Current income taxes	5,686		8,823
Advance billings	237,709		257,766
Liabilities of discontinued operations	84,219		72,808
Deferred taxes on income	234,190		234,643
Other noncurrent liabilities	461,074		519,079
Stockholders’ equity:
Total stockholders’ equity	195,917		188,561	$ 29,373	$ (103,660)
Retained earnings	5,248,991		5,229,584
Accumulated other comprehensive loss	(810,251)		$ (792,173)
ASC 606
Stockholders’ equity:
Retained earnings		$ (9,000)
Prior guidance | ASC 606
ASSETS
Total assets	6,250,943
Accounts receivable (net of allowance of $13,515 and $14,786, respectively)	407,204
Current income taxes	39,298
Other current assets and prepayments	102,760
Assets of discontinued operations	312,922
Noncurrent income taxes	54,429
Other assets	533,886
Total Liabilities
Total liabilities	6,062,221
Accounts payable and accrued liabilities	1,347,837
Current income taxes	43
Advance billings	250,948
Liabilities of discontinued operations	84,132
Deferred taxes on income	238,539
Other noncurrent liabilities	462,110
Stockholders’ equity:
Total stockholders’ equity	188,722
Retained earnings	5,241,824
Accumulated other comprehensive loss	(810,279)
Total increase (decrease) | ASC 606
ASSETS
Total assets	(4,192)
Accounts receivable (net of allowance of $13,515 and $14,786, respectively)	1,499
Current income taxes	(198)
Other current assets and prepayments	(656)
Assets of discontinued operations	434
Noncurrent income taxes	(330)
Other assets	(4,941)
Total Liabilities
Total liabilities	(11,387)
Accounts payable and accrued liabilities	1,507
Current income taxes	5,643
Advance billings	(13,239)
Liabilities of discontinued operations	87
Deferred taxes on income	(4,349)
Other noncurrent liabilities	(1,036)
Stockholders’ equity:
Total stockholders’ equity	7,195
Retained earnings	7,167
Accumulated other comprehensive loss	$ 28