Segment Reporting (Revenue and Adjusted EBITDA for each Reportable Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net revenue	$ 755,936		$ 1,450,120
Adjusted EBITDA	231,841		428,696
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Income (loss) before income tax provision (benefit)	(56,010)	$ (107,555)	(128,165)	$ (147,255)
Amortization of capitalized software developed for sale	12		89
Depreciation and amortization	146,869		285,409
Interest expense	61,627		124,294
Equity compensation	14,331		23,914
Acquisition accounting adjustments	34,686		83,225
Acquisition and divestiture-related costs	2,337		7,458
Integration and related costs	7,536		17,894
Strategic initiatives, duplicative and transition costs	3,765		8,845
Severance costs	3,172		7,876
Accretion and changes in estimate with related parties, net	5,293		11,188
Impairment of long-lived assets and other	7,447		13,760
Gain on sale of businesses	(176)		(28,270)
Contingent consideration	(550)		(3,000)
Loss on extinguishment of debt	1,489		1,489
Other non-routine, net	13		2,690
Adjusted EBITDA	231,841		428,696
Postage and Eliminations [Member]
Segment Reporting Information [Line Items]
Net revenue	24,073		51,136
Purchase Accounting Adjustment [Member]
Segment Reporting Information [Line Items]
Net revenue	(38,909)		(93,909)
Software and Analytics [Member]
Segment Reporting Information [Line Items]
Net revenue	354,860		746,449
Adjusted EBITDA	117,393		261,325
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	117,393		261,325
Network Solutions [Member]
Segment Reporting Information [Line Items]
Net revenue	184,095		326,921
Adjusted EBITDA	94,508		165,011
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	94,508		165,011
Technology-Enabled Services [Member]
Segment Reporting Information [Line Items]
Net revenue	231,817		419,523
Adjusted EBITDA	19,940		2,360
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	19,940		2,360
Postage [Member]
Segment Reporting Information [Line Items]
Net revenue	50,023		95,795
Postage [Member] | Postage and Eliminations [Member]
Segment Reporting Information [Line Items]
Net revenue	$ 50,023		$ 95,795