Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Income Taxes [Line Items]
Deferred tax liability	$ 563,606	$ 605,291
Valuation allowance	22,076	20,238
Reduction to income tax expense if benefits from net operating loss carryforwards are realized	22,076
Unrecognized tax benefits that would affect the effective tax rate	57,723
Interest and penalties	42	$ 121	$ 138
Accelerated receipt of AMT credit refund amount	869
Deferred tax liability	28,576
Residual Deferred Tax Asset [Member]
Income Taxes [Line Items]
Valuation allowance	5,449
Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards	836,227
Federal [Member] | Research and Development Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards	43,862
State [Member]
Income Taxes [Line Items]
Operating loss carryforwards	1,365,807
State [Member] | Research and Development Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards	1,849
Foreign [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 6,337
Operating loss carryforwards, expiration date	Dec. 31, 2024
State and Foreign [Member]
Income Taxes [Line Items]
Valuation allowance	$ 16,627
Minimum [Member] | Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2032
Minimum [Member] | Federal [Member] | Research and Development Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards, expiration date	Dec. 31, 2038
Minimum [Member] | State [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2023
Maximum [Member] | Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2037
Maximum [Member] | Federal [Member] | Research and Development Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards, expiration date	Dec. 31, 2042
Maximum [Member] | State [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2041