Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Recently Adopted and Issued Accounting Pronouncements) (Details 1) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Item Effected [Line Items]
Accounts receivable, net	$ 582,280	$ 622,461	$ 620,319
Inventories and contracts in progress	69,477	60,858	60,612
Other current assets	82,723	72,596	66,253
Accounts payable and accrued liabilities	486,578	526,411	526,323
Deferred revenue	308,728	339,108	339,454
Deferred income taxes	322,421	364,767	362,701
Retained earnings	$ 6,236,125	5,798,647	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		246
Other current assets		6,343
Accounts payable and accrued liabilities		88
Deferred revenue		(346)
Deferred income taxes		2,066
Retained earnings		$ 6,923