Segment Reporting (Revenue and Adjusted EBITDA for each Reportable Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Net revenue	$ 826,764	$ 755,936	$ 1,694,620	$ 1,450,120
Adjusted EBITDA	246,462	231,841	529,190	428,696
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Income (loss) before income tax provision (benefit)	(53,153)	(56,010)	(65,207)	(128,165)
Amortization of capitalized software developed for sale	859	12	1,576	89
Depreciation and amortization	163,469	146,869	331,681	285,409
Interest expense	59,466	61,627	118,852	124,294
Equity compensation	23,745	14,331	49,911	23,914
Acquisition accounting adjustments	(1,653)	34,686	(2,212)	83,225
Acquisition and divestiture-related costs	13,765	2,337	20,159	7,458
Integration and related costs	5,933	7,536	17,301	17,894
Strategic initiatives, duplicative and transition costs	14,644	3,765	24,572	8,845
Severance costs	7,303	3,172	12,023	7,876
Accretion and changes in estimate, net	4,355	5,293	9,087	11,188
Impairment of long-lived assets and other	81	7,447	1,692	13,760
Loss on extinguishment of debt	2,232	1,489	2,232	1,489
Gain on sale of businesses		(176)		(28,270)
Contingent consideration		(550)		(3,000)
Other non-routine, net	5,416	13	7,523	2,690
Adjusted EBITDA	246,462	231,841	529,190	428,696
Postage and Eliminations [Member]
Segment Reporting Information [Line Items]
Net revenue	19,091	24,073	36,109	51,136
Purchase Accounting Adjustment [Member]
Segment Reporting Information [Line Items]
Net revenue	(3,278)	(38,909)	(7,740)	(93,909)
Software and Analytics [Member]
Segment Reporting Information [Line Items]
Net revenue	363,423	354,860	783,740	746,449
Adjusted EBITDA	112,318	117,393	272,683	261,325
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	112,318	117,393	272,683	261,325
Network Solutions [Member]
Segment Reporting Information [Line Items]
Net revenue	215,600	184,095	425,061	326,921
Adjusted EBITDA	112,986	94,508	222,474	165,011
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	112,986	94,508	222,474	165,011
Technology-Enabled Services [Member]
Segment Reporting Information [Line Items]
Net revenue	231,928	231,817	457,450	419,523
Adjusted EBITDA	21,158	19,940	34,033	2,360
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	21,158	19,940	34,033	2,360
Postage [Member]
Segment Reporting Information [Line Items]
Net revenue	$ 52,550	$ 50,023	$ 103,758	$ 95,795