Derivative Financial Instruments Outstanding Interest Rate Swap Agreements (Details) - USD ($) $ in Thousands		6 Months Ended
	Sep. 30, 2016	Jun. 30, 2015
Interest Rate Swap 3 [Member]
Derivative [Line Items]
Effective Date		Sep. 30, 2014
Expiration Date		Sep. 30, 2015
Interest Rate Swap 3 [Member] | Notional Period 1 [Member]
Derivative [Line Items]
Notional Amount		$ 1,150,000
Pay Fixed Rate		0.54%
Interest Rate Swap 3 [Member] | Notional Period 2 [Member]
Derivative [Line Items]
Notional Amount		$ 1,100,000
Pay Fixed Rate		0.54%
Interest Rate Swap 3 [Member] | Notional Period 3 [Member]
Derivative [Line Items]
Notional Amount		$ 1,050,000
Pay Fixed Rate		0.54%
Interest Rate Swap 3 [Member] | Notional Period 4 [Member]
Derivative [Line Items]
Notional Amount		$ 1,000,000
Pay Fixed Rate		0.54%
Interest Rate Swap 4 [Member]
Derivative [Line Items]
Effective Date		Sep. 30, 2015
Expiration Date		Sep. 30, 2016
Interest Rate Swap 4 [Member] | Notional Period 1 [Member]
Derivative [Line Items]
Notional Amount		$ 350,000
Pay Fixed Rate		0.93%
Interest Rate Swap 5 [Member]
Derivative [Line Items]
Effective Date		Sep. 30, 2016
Expiration Date		Sep. 30, 2026
Interest Rate Swap 5 [Member] | Notional Period 1 [Member]
Derivative [Line Items]
Notional Amount		$ 100,000
Pay Fixed Rate		2.79%
Interest Rate Swap 6 [Member]
Derivative [Line Items]
Effective Date		Sep. 30, 2016
Expiration Date		Sep. 30, 2026
Interest Rate Swap 6 [Member] | Notional Period 1 [Member]
Derivative [Line Items]
Notional Amount		$ 100,000
Pay Fixed Rate		2.79%
Interest Rate Swap 7 [Member]
Derivative [Line Items]
Effective Date		Sep. 30, 2016
Expiration Date		Sep. 30, 2026
Interest Rate Swap 7 [Member] | Notional Period 1 [Member]
Derivative [Line Items]
Notional Amount		$ 100,000
Pay Fixed Rate		2.80%
Scenario, Forecast [Member]
Derivative [Line Items]
Derivative settlement date	Sep. 30, 2016
Variable rate debt [Member] | Scenario, Forecast [Member]
Derivative [Line Items]
Probable future debt	$ 300,000
Fixed rate debt [Member] | Scenario, Forecast [Member]
Derivative [Line Items]
Probable future debt	$ 300,000