Derivative Financial Instruments Outstanding Interest Rate Swap Agreements (Details) (USD $)	9 Months Ended					9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		0 Months Ended
	Sep. 30, 2014 Interest Rate Swap 3 [Member]	Sep. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 1 [Member]	Sep. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 2 [Member]	Sep. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 3 [Member]	Sep. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 4 [Member]	Sep. 30, 2014 Interest Rate Swap 4 [Member]	Sep. 30, 2014 Interest Rate Swap 4 [Member] Notional Period 1 [Member]	Sep. 30, 2014 Interest Rate Swap 5 [Member]	Sep. 30, 2014 Interest Rate Swap 5 [Member] Notional Period 1 [Member]	Sep. 30, 2014 Interest Rate Swap 6 [Member]	Sep. 30, 2014 Interest Rate Swap 6 [Member] Notional Period 1 [Member]	Sep. 30, 2014 Interest Rate Swap 7 [Member]	Sep. 30, 2014 Interest Rate Swap 7 [Member] Notional Period 1 [Member]	Sep. 30, 2016 Scenario, Forecast [Member]	Sep. 30, 2016 Fixed rate debt [Member] Scenario, Forecast [Member]	Sep. 30, 2016 Variable rate debt [Member] Scenario, Forecast [Member]
Derivatives [Line Items]
Effective date	Sep. 30, 2014					Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2016		Sep. 30, 2016
Expiration date	Sep. 30, 2015					Sep. 30, 2016		Sep. 30, 2026		Sep. 30, 2026		Sep. 30, 2026
Notional amount		$ 1,150,000,000	$ 1,100,000,000	$ 1,050,000,000	$ 1,000,000,000		$ 350,000,000		$ 100,000,000		$ 100,000,000		$ 100,000,000
Pay fixed rate, forward interest rate		0.54%	0.54%	0.54%	0.54%		0.93%		2.79%		2.79%		2.80%
Probable future debt															$ 300,000,000	$ 300,000,000
Derivative settlement date														Sep. 30, 2016