Organization, Basis of Presentation and Recent Accounting Pronouncements (Recent Accounting Pronouncements) (Details 1) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Item Effected [Line Items]
Accounts receivable, net	$ 540,593	$ 622,461	$ 620,319
Inventories and contracts in progress	66,949	61,515	60,612
Other current assets	88,956	72,596	66,253
Accounts payable and accrued liabilities	435,498	526,411	526,323
Deferred revenue	294,519	339,108	339,454
Deferred income taxes		364,898
Retained earnings	$ 6,022,315	5,799,173	5,791,724
Accounting Standards Update 2014-09 [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Item Effected [Line Items]
Accounts receivable, net			620,319
Inventories and contracts in progress			60,612
Other current assets			66,253
Accounts payable and accrued liabilities			526,323
Deferred revenue			339,454
Deferred income taxes			362,701
Retained earnings			$ 5,791,724
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Item Effected [Line Items]
Accounts receivable, net		2,142
Inventories and contracts in progress		903
Other current assets		6,343
Accounts payable and accrued liabilities		88
Deferred revenue		(346)
Deferred income taxes		2,197
Retained earnings		$ 7,449