Revenue from Contracts with Customers (Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 947,140	$ 832,856	$ 861,436	$ 880,948	$ 916,406	$ 733,273	$ 730,413	$ 743,180	$ 3,522,380	$ 3,123,272	$ 2,981,323
Total from contracts with customers									2,629,541
Costs and expenses:
Total costs and expenses									3,310,019	2,901,357	2,779,534
Selling, general and administrative									1,123,116	1,170,905	1,140,100
Income before income taxes									212,361
ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers									2,629,541
Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									3,483,757
Costs and expenses:
Total costs and expenses									3,318,288
Selling, general and administrative									1,135,543
Income before income taxes									165,469
Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									38,623
Costs and expenses:
Total costs and expenses									(8,269)
Selling, general and administrative									(12,427)
Income before income taxes									46,892
Equipment sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									430,451	476,691	480,031
Total from contracts with customers									112,056
Costs and expenses:
Cost of products and sales									181,766	201,116	203,220
Equipment sales | Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									432,911
Costs and expenses:
Cost of products and sales									181,957
Equipment sales | Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									(2,460)
Costs and expenses:
Cost of products and sales									(191)
Software
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers									340,855	331,843	325,577
Costs and expenses:
Cost of products and sales									100,681	95,033	96,151
Software | ASC 606
Costs and expenses:
Cost of products and sales									43,000
Software | Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers									297,976
Costs and expenses:
Cost of products and sales									96,332
Software | Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers									42,879
Costs and expenses:
Cost of products and sales									4,349
Business services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers									1,561,522	1,068,426	827,676
Costs and expenses:
Cost of products and sales									1,246,084	$ 773,052	$ 568,509
Business services | Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers									1,563,318
Business services | Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers									$ (1,796)