Related Party Transactions (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) $ / employee	Dec. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)
Related Party Transaction [Line Items]
Long-term debt, excluding current portion	$ 4,780,828		$ 4,780,828		$ 4,710,294
Option Agreement [Member[ | McKesson Corporation [Member]
Related Party Transaction [Line Items]
Maximum percentage of ownership in the outstanding units of the Joint Venture allowed for option to acquire can be exercised			5.00%
Transition Services Agreements [Member]
Related Party Transaction [Line Items]
Transition fee income	0	$ 0	$ 283	$ 0
Employer Healthcare Program Agreement [Member]
Related Party Transaction [Line Items]
Service fee per participating employee per month | $ / employee			1.00
Senior Credit Facilities [Member] | GSO-Managed Funds [Member]
Related Party Transaction [Line Items]
Long-term debt, excluding current portion	$ 168,200		$ 168,200		$ 151,301