Revenue - Schedule of Net Sales Disaggregated by Major Product Line and Reportable Segments (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
Total net sales	$ 564,118	$ 510,580	$ 546,430	$ 542,832	$ 544,770	$ 543,275	$ 556,082	$ 522,760	$ 2,163,960	$ 2,166,887	$ 2,239,557
Hardware & Software Products [Member] | Consolidated [Member]
Total net sales									1,985,767	2,006,049
Services [Member] | Consolidated [Member]
Total net sales									178,193	160,838
Commercial [Member]
Total net sales									1,647,431	1,709,249	1,737,830
Commercial [Member] | Hardware & Software Products [Member]
Total net sales									1,522,440	1,592,920
Commercial [Member] | Services [Member]
Total net sales									124,991	116,329
Public Sector [Member]
Total net sales									258,945	274,650	351,617
Public Sector [Member] | Hardware & Software Products [Member]
Total net sales									241,148	260,740
Public Sector [Member] | Services [Member]
Total net sales									17,797	13,910
Canada [Member]
Total net sales									195,846	171,208	150,193
Canada [Member] | Hardware & Software Products [Member]
Total net sales									165,286	141,126
Canada [Member] | Services [Member]
Total net sales									30,560	30,082
United Kingdom [Member]
Total net sales									62,359	12,235
United Kingdom [Member] | Hardware & Software Products [Member]
Total net sales									57,514	11,718
United Kingdom [Member] | Services [Member]
Total net sales									4,845	517
Corporate & Other [Member]
Total net sales									(621)	(455)	(83)
Corporate & Other [Member] | Hardware & Software Products [Member]
Total net sales									(621)	(455)
Corporate & Other [Member] | Services [Member]
Total net sales
Consolidated [Member]
Total net sales									$ 2,163,960	$ 2,166,887	$ 2,239,557