Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 1,467,976	$ 1,368,673	$ 4,312,509	$ 4,110,763
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,375,455	1,276,406	4,049,892	3,848,618
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	92,521	92,267	262,617	262,145
Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	1,285,488	1,230,769	3,774,507	3,645,397
Domestic Segment | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,200,015	1,143,515	3,542,178	3,410,827
Domestic Segment | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	85,473	87,254	232,329	234,570
International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	182,488	137,904	538,002	465,366
International Segment [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	175,440	132,891	507,714	437,791
International Segment [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,048	5,013	30,288	27,575
Revenue, Licensed Software, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	199,179	171,694	535,956	481,888
Revenue, Licensed Software, Net [Member] | Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	186,106	159,327	492,847	444,774
Revenue, Licensed Software, Net [Member] | International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	13,073	12,367	43,109	37,114
Revenue, Technology Resale, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	37,584	47,113	140,116	140,717
Revenue, Technology Resale, Net [Member] | Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	35,206	45,217	124,777	126,042
Revenue, Technology Resale, Net [Member] | International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,378	1,896	15,339	14,675
Revenue, Subscriptions, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	91,771	93,407	290,020	279,844
Revenue, Subscriptions, Net [Member] | Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	87,490	87,878	277,095	260,095
Revenue, Subscriptions, Net [Member] | International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,281	5,529	12,925	19,749
Revenue, Professional Services, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	551,748	479,895	1,583,248	1,452,323
Revenue, Professional Services, Net [Member] | Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	472,387	433,127	1,364,450	1,295,759
Revenue, Professional Services, Net [Member] | International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	79,361	46,768	218,798	156,564
Revenue, Managed Services, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	323,132	311,844	961,285	928,356
Revenue, Managed Services, Net [Member] | Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	286,038	280,827	852,872	836,242
Revenue, Managed Services, Net [Member] | International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	37,094	31,017	108,413	92,114
Revenue, Support and Maintenance Services, Net [Member]
Disaggregation of Revenue [Line Items]
Revenues	257,025	259,978	780,024	807,695
Revenue, Support and Maintenance Services, Net [Member] | Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	210,864	219,682	640,349	663,399
Revenue, Support and Maintenance Services, Net [Member] | International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	46,161	40,296	139,675	144,296
Revenue, Reimbursement Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,537	4,742	21,860	19,940
Revenue, Reimbursement Revenue [Member] | Domestic Segment
Disaggregation of Revenue [Line Items]
Revenues	7,397	4,711	22,117	19,086
Revenue, Reimbursement Revenue [Member] | International Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 140	$ 31	$ (257)	$ 854