Revenue from Contracts with Customers (Income Statement) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 832,856	$ 733,273	$ 2,575,240	$ 2,206,866
Total from contracts with customers	614,105		1,907,892
Costs and expenses:
Total costs and expenses	787,727	677,008	2,415,358	2,023,844
Selling, general and administrative	269,387	288,093	847,281	861,738
Income before income taxes	45,129	56,265	159,882	183,022
(Benefit) provision for income taxes	(1,976)	10,828	20,745	38,700
Net income from continuing operations	$ 47,105	$ 45,437	$ 139,137	$ 144,322
Earnings per share:
Basic earnings - continuing operations (in dollars per share)	$ 0.25	$ 0.24	$ 0.74	$ 0.77
Diluted earnings per share - continuing operations (in dollars per share)	$ 0.25	$ 0.24	$ 0.74	$ 0.77
ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers	$ 614,105		$ 1,907,892
Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	828,999		2,553,059
Costs and expenses:
Total costs and expenses	790,565		2,420,406
Selling, general and administrative	272,955		854,972
Income before income taxes	38,434		132,653
(Benefit) provision for income taxes	(3,768)		13,666
Net income from continuing operations	$ 42,202		$ 118,987
Earnings per share:
Basic earnings - continuing operations (in dollars per share)	$ 0.22		$ 0.63
Diluted earnings per share - continuing operations (in dollars per share)	$ 0.22		$ 0.63
Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 3,857		$ 22,181
Costs and expenses:
Total costs and expenses	(2,838)		(5,048)
Selling, general and administrative	(3,568)		(7,691)
Income before income taxes	6,695		27,229
(Benefit) provision for income taxes	1,792		7,079
Net income from continuing operations	$ 4,903		$ 20,150
Earnings per share:
Basic earnings - continuing operations (in dollars per share)	$ 0.03		$ 0.11
Diluted earnings per share - continuing operations (in dollars per share)	$ 0.03		$ 0.11
Equipment sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 100,937	$ 103,514	$ 317,058	$ 349,401
Total from contracts with customers	25,589		83,053
Costs and expenses:
Cost of products and sales	39,353	49,328	132,513	145,450
Equipment sales | Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	101,632		319,165
Costs and expenses:
Cost of products and sales	39,409		132,628
Equipment sales | Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	(695)		(2,107)
Costs and expenses:
Cost of products and sales	(56)		(115)
Software
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers	76,026	94,226	244,022	248,391
Costs and expenses:
Cost of products and sales	24,743	24,107	75,257	70,622
Software | ASC 606
Costs and expenses:
Cost of products and sales	5,000		26,000
Software | Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers	71,081		218,410
Costs and expenses:
Cost of products and sales	23,957		72,499
Software | Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers	4,945		25,612
Costs and expenses:
Cost of products and sales	786		2,758
Income before income taxes	4,000		23,000
Business services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers	363,528	229,711	1,117,942	672,133
Costs and expenses:
Cost of products and sales	291,650	$ 166,984	882,529	$ 470,890
Business services | Prior guidance | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers	363,921		1,119,266
Business services | Increase (decrease) | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total from contracts with customers	$ (393)		$ (1,324)