Operating Segments - Operating Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Depreciation expense	$ 11,700	$ 11,700	$ 35,600	$ 34,600
Amortization of intangibles	25,533	27,162	74,990	77,944
Severance, restructuring, and acquisition integration costs	11,688	16,679	57,010	32,839
Segment assets	3,714,912		3,714,912		$ 3,840,613
Enterprise Solutions
Segment Reporting Information [Line Items]
Severance, restructuring, and acquisition integration costs	9,528	9,309	46,949	23,701
Industrial Solutions
Segment Reporting Information [Line Items]
Severance, restructuring, and acquisition integration costs	2,160	7,370	10,061	9,138
Reportable Segment
Segment Reporting Information [Line Items]
Segment revenues	659,003	621,745	1,937,867	1,783,759
Affiliate revenues	1,791	973	4,379	4,135
Segment EBITDA	125,960	117,856	353,344	321,748
Depreciation expense	11,671	11,683	35,562	34,594
Amortization of intangibles	25,533	27,162	74,990	77,944
Amortization of software development intangible assets	620	0	1,344	0
Severance, restructuring, and acquisition integration costs	11,688	16,679	57,010	32,839
Purchase accounting effects of acquisitions	821	2,922	2,359	4,089
Deferred revenue adjustments	3,229	0	7,889	0
Segment assets	1,215,131	1,058,713	1,215,131	1,058,713
Reportable Segment | Enterprise Solutions
Segment Reporting Information [Line Items]
Segment revenues	392,080	360,842	1,142,765	1,023,924
Affiliate revenues	1,776	971	4,318	4,084
Segment EBITDA	72,210	62,109	199,943	168,073
Depreciation expense	7,092	6,828	21,465	20,129
Amortization of intangibles	12,322	13,920	35,301	38,241
Amortization of software development intangible assets	620		1,344
Severance, restructuring, and acquisition integration costs	9,528	9,309	46,949	23,701
Purchase accounting effects of acquisitions	821	2,922	2,359	4,089
Deferred revenue adjustments	3,229		7,889
Segment assets	766,505	658,175	766,505	658,175
Reportable Segment | Industrial Solutions
Segment Reporting Information [Line Items]
Segment revenues	266,923	260,903	795,102	759,835
Affiliate revenues	15	2	61	51
Segment EBITDA	53,750	55,747	153,401	153,675
Depreciation expense	4,579	4,855	14,097	14,465
Amortization of intangibles	13,211	13,242	39,689	39,703
Amortization of software development intangible assets	0		0
Severance, restructuring, and acquisition integration costs	2,160	7,370	10,061	9,138
Purchase accounting effects of acquisitions	0	0	0	0
Deferred revenue adjustments	0		0
Segment assets	$ 448,626	$ 400,538	$ 448,626	$ 400,538