Sales Recognition - Summary of Revenue Disaggregated by Reportable Operating Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	$ 2,144,051	$ 1,685,466
Gross Revenue Recognition (Principal) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	2,038,527	1,597,109
Net Revenue Recognition (Agent) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	105,524	88,357
Large Enterprise / Corporate [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	1,466,061	1,250,755
Public Sector [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	260,518	232,337
Small and Medium-Sized Businesses [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	417,472	202,374
North America Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	1,674,381	1,242,441
North America Segment [Member] | Gross Revenue Recognition (Principal) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	1,600,514	1,182,078
North America Segment [Member] | Net Revenue Recognition (Agent) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	73,867	60,363
North America Segment [Member] | Large Enterprise / Corporate [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	1,160,748	976,841
North America Segment [Member] | Public Sector [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	127,557	97,117
North America Segment [Member] | Small and Medium-Sized Businesses [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	386,076	168,483
EMEA Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	418,886	390,175
EMEA Segment [Member] | Gross Revenue Recognition (Principal) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	392,259	367,165
EMEA Segment [Member] | Net Revenue Recognition (Agent) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	26,627	23,010
EMEA Segment [Member] | Large Enterprise / Corporate [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	292,288	260,607
EMEA Segment [Member] | Public Sector [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	108,856	109,066
EMEA Segment [Member] | Small and Medium-Sized Businesses [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	17,742	20,502
APAC Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	50,784	52,850
APAC Segment [Member] | Gross Revenue Recognition (Principal) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	45,754	47,866
APAC Segment [Member] | Net Revenue Recognition (Agent) [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	5,030	4,984
APAC Segment [Member] | Large Enterprise / Corporate [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	13,025	13,307
APAC Segment [Member] | Public Sector [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	24,105	26,154
APAC Segment [Member] | Small and Medium-Sized Businesses [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	13,654	13,389
Hardware Net Sales [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	1,311,201	926,380
Hardware Net Sales [Member] | North America Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	1,128,486	748,337
Hardware Net Sales [Member] | EMEA Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	174,969	171,525
Hardware Net Sales [Member] | APAC Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	7,746	6,518
Software Net Sales [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	537,115	540,292
Software Net Sales [Member] | North America Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	305,163	322,079
Software Net Sales [Member] | EMEA Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	201,082	183,148
Software Net Sales [Member] | APAC Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	30,870	35,065
Services Net Sales [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	295,735	218,794
Services Net Sales [Member] | North America Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	240,732	172,025
Services Net Sales [Member] | EMEA Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	42,835	35,502
Services Net Sales [Member] | APAC Segment [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	$ 12,168	$ 11,267