Segment Reporting (Revenue and Adjusted EBITDA for each Reportable Segment) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net revenue	$ 785,141			$ 2,235,261
Adjusted EBITDA	233,424			662,119
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Income (loss) before income tax provision (benefit)	(2,366)		$ 65,975	(130,531)	$ (81,280)
Amortization of capitalized software developed for sale	460			550
Depreciation and amortization	151,143			436,552
Interest expense	61,439		$ 1	185,733	$ 1
Equity compensation	10,944			34,858
Acquisition accounting adjustments	20,601			103,826
Acquisition and divestiture-related costs	2,661			10,119
Integration and related costs	9,688			27,581
Strategic initiatives, duplicative and transition costs	4,324			13,169
Severance costs	2,591			10,467
Accretion and changes in estimate, net	(2,759)			8,429
Impairment of long-lived assets and other	658			14,418
Gain on sale of businesses	(32,217)			(60,487)
Contingent consideration				(3,000)
Loss on extinguishment of debt	6,145	$ 1,489		7,634
Other non-routine, net	112			2,801
Adjusted EBITDA	233,424			662,119
Postage and Eliminations [Member]
Segment Reporting Information [Line Items]
Net revenue	22,006			73,142
Purchase Accounting Adjustment [Member]
Segment Reporting Information [Line Items]
Net revenue	(24,179)			(118,088)
Software and Analytics [Member]
Segment Reporting Information [Line Items]
Net revenue	372,212			1,118,661
Adjusted EBITDA	120,779			382,103
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	120,779			382,103
Network Solutions [Member]
Segment Reporting Information [Line Items]
Net revenue	192,588			519,509
Adjusted EBITDA	103,847			268,858
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	103,847			268,858
Technology-Enabled Services [Member]
Segment Reporting Information [Line Items]
Net revenue	222,514			642,037
Adjusted EBITDA	8,798			11,158
Reconciliation of income (loss) before tax provision (benefit) to Adjusted EBITDA
Adjusted EBITDA	8,798			11,158
Postage [Member]
Segment Reporting Information [Line Items]
Net revenue	49,877			145,672
Postage [Member] | Postage and Eliminations [Member]
Segment Reporting Information [Line Items]
Net revenue	$ 49,877			$ 145,672