Segment Reporting (Revenue and Adjusted EBITDA for each Reportable Segment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net revenue	$ 3,090,421	$ 196,792
Adjusted EBITDA	934,165
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Income (loss) before income tax provision (benefit)	(147,397)	(1,090,851)	$ (70,607)
Amortization of capitalized software developed for sale	1,326
Depreciation and amortization	591,048	30,838
Interest expense	245,241	16,652
Equity compensation	59,016
Acquisition accounting adjustments	109,743
Acquisition and divestiture-related costs	19,709
Integration and related costs	40,675
Strategic initiatives, duplicative and transition costs	21,841
Severance costs	13,184
Accretion and changes in estimate, net	11,644	15,823
Impairment of long-lived assets and other	18,190
Gain on sale of businesses	(59,143)
Contingent consideration	(3,000)
Loss on extinguishment of debt	8,924
Other non-routine, net	3,164
Adjusted EBITDA	934,165
Postage and Eliminations [Member]
Segment Reporting Information [Line Items]
Net revenue	96,533
Purchase Accounting Adjustment [Member]
Segment Reporting Information [Line Items]
Net revenue	(128,230)
Software and Analytics [Member]
Segment Reporting Information [Line Items]
Net revenue	1,534,926
Adjusted EBITDA	526,129
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	526,129
Network Solutions [Member]
Segment Reporting Information [Line Items]
Net revenue	717,843
Adjusted EBITDA	377,005
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	377,005
Technology-Enabled Services [Member]
Segment Reporting Information [Line Items]
Net revenue	869,349
Adjusted EBITDA	31,031
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	31,031
Postage [Member]
Segment Reporting Information [Line Items]
Net revenue	$ 196,532	$ 12,631