Revenues - Products and Services (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 2,585,368	$ 2,388,643	$ 2,356,672
Enterprise Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,515,566	1,356,305	1,371,808
Industrial Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,069,802	1,032,338	984,864
Products
Disaggregation of Revenue [Line Items]
Revenues	2,415,786	2,211,223	2,178,600
Products | Enterprise Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,441,757	1,281,960	1,293,392
Products | Industrial Solutions
Disaggregation of Revenue [Line Items]
Revenues	974,029	929,263	885,208
Support And Services
Disaggregation of Revenue [Line Items]
Revenues	169,582	177,420	178,072
Support And Services | Enterprise Solutions
Disaggregation of Revenue [Line Items]
Revenues	73,809	74,345	78,416
Support And Services | Industrial Solutions
Disaggregation of Revenue [Line Items]
Revenues	$ 95,773	$ 103,075	$ 99,656