Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Taxes [Line Items]
Deferred tax liability	$ 615,904	$ 159,993
Valuation allowance	29,350
Reduction to income tax expense if benefits from net operating loss carryforwards are realized	26,403
Unrecognized tax benefits that would affect the effective tax rate	46,672
Interest and penalties	138	$ 0	$ 0
Accelerated receipt of AMT credit refund amount	869
Residual Deferred Tax Asset [Member]
Income Taxes [Line Items]
Valuation allowance	12,701
Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards	1,174,862
Federal [Member] | Research and Development Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards	16,302
State [Member]
Income Taxes [Line Items]
Operating loss carryforwards	1,833,161
State [Member] | Research and Development Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards	413
State [Member] | Research and Development Tax Credit Carryforward [Member] | Indefinite Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards	116
State [Member] | Research and Development Tax Credit Carryforward [Member] | Expire from 2033 through 2034 [Member]
Income Taxes [Line Items]
Tax credit carryforwards	197
Foreign [Member]
Income Taxes [Line Items]
Operating loss carryforwards	15,260
State and Foreign [Member]
Income Taxes [Line Items]
Valuation allowance	17,279
Accounting Standards Update 2017-01 [Member]
Income Taxes [Line Items]
Deferred tax liability	$ (28,576)
Minimum [Member] | Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2026
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, 2020
Minimum [Member] | State [Member] | Research and Development Tax Credit Carryforward [Member] | Expire from 2033 through 2034 [Member]
Income Taxes [Line Items]
Tax credit carryforwards, expiration date	Dec. 31, 2033
Minimum [Member] | Foreign [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2028
Maximum [Member] | Federal [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2040
Maximum [Member] | Federal [Member] | Research and Development Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforwards, expiration date	Dec. 31, 2040
Maximum [Member] | State [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2040
Maximum [Member] | State [Member] | Research and Development Tax Credit Carryforward [Member] | Expire from 2033 through 2034 [Member]
Income Taxes [Line Items]
Tax credit carryforwards, expiration date	Dec. 31, 2035
Maximum [Member] | Foreign [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2037