Revenue - Schedule of Net Sales Disaggregated by Major Product Line and Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Total net sales	$ 533,989	$ 542,832
Hardware & Software Products [Member] | Consolidated [Member]
Total net sales	490,013	497,804
Services [Member] | Consolidated [Member]
Total net sales	43,976	45,028
Commercial [Member]
Total net sales	428,528	414,731
Commercial [Member] | Hardware & Software Products [Member]
Total net sales	397,034	381,769
Commercial [Member] | Services [Member]
Total net sales	31,494	32,962
Public Sector [Member]
Total net sales	40,047	56,062
Public Sector [Member] | Hardware & Software Products [Member]
Total net sales	36,903	52,921
Public Sector [Member] | Services [Member]
Total net sales	3,144	3,141
Canada [Member]
Total net sales	47,193	54,120
Canada [Member] | Hardware & Software Products [Member]
Total net sales	39,007	46,600
Canada [Member] | Services [Member]
Total net sales	8,186	7,520
United Kingdom [Member]
Total net sales	18,374	18,073
United Kingdom [Member] | Hardware & Software Products [Member]
Total net sales	17,222	16,668
United Kingdom [Member] | Services [Member]
Total net sales	1,152	1,405
Corporate & Other [Member]
Total net sales	(153)	(154)
Corporate & Other [Member] | Hardware & Software Products [Member]
Total net sales	(153)	(154)
Corporate & Other [Member] | Services [Member]
Total net sales
Consolidated [Member]
Total net sales	$ 533,989	$ 542,832