Interest Rate Cap Agreements (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Sep. 30, 2020	Mar. 31, 2021	Mar. 31, 2020	Aug. 31, 2018
Derivative [Line Items]
Fair value derivative net liability	$ 40,314
Forecast [Member]
Derivative [Line Items]
Reclassified as interest expense		$ 1,604
Interest Rate Cap Agreements [Member]
Derivative [Line Items]
Notional amount			$ 1,000,000
Effective date	Mar. 31, 2020
Derivative, maturity date	Mar. 31, 2024
Interest Rate Cap Agreements [Member] | Maximum [Member]
Derivative [Line Items]
Variable rate			1.00%
Joint Venture [Member] | Interest Rate Cap Agreements [Member]
Derivative [Line Items]
Notional amount			$ 1,500,000
Effective date	Aug. 31, 2018
Derivative, maturity date	Dec. 31, 2021
Joint Venture [Member] | Interest Rate Cap Agreements [Member] | Minimum [Member]
Derivative [Line Items]
Notional amount				$ 500,000
Joint Venture [Member] | Interest Rate Cap Agreements [Member] | Maximum [Member]
Derivative [Line Items]
Notional amount				$ 1,500,000
Variable rate				1.00%