Derivative Financial Instruments Expired Interest Rate Swap Agreements (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Interest Rate Swap 8 [Member]
Derivatives [Line Items]
Effective Date	Oct. 06, 2008
Expiration Date	Sep. 30, 2013
Interest Rate Swap 8 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Notional Amount	120,000
Pay Fixed Rate	3.88%
Interest Rate Swap 1 [Member]
Derivatives [Line Items]
Effective Date	Oct. 04, 2012
Expiration Date	Sep. 30, 2013
Interest Rate Swap 1 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Notional Amount	1,450,000
Pay Fixed Rate	0.25%
Interest Rate Swap 1 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Notional Amount	1,350,000
Pay Fixed Rate	0.25%
Interest Rate Swap 1 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Notional Amount	1,300,000
Pay Fixed Rate	0.25%
Interest Rate Swap 1 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Notional Amount	1,250,000
Pay Fixed Rate	0.25%
Interest Rate Swap 2 [Member]
Derivatives [Line Items]
Effective Date	Sep. 30, 2013
Expiration Date	Sep. 30, 2014
Interest Rate Swap 2 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Notional Amount	1,350,000
Pay Fixed Rate	0.35%
Interest Rate Swap 2 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Notional Amount	1,300,000
Pay Fixed Rate	0.35%
Interest Rate Swap 2 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Notional Amount	1,250,000
Pay Fixed Rate	0.35%
Interest Rate Swap 2 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Notional Amount	1,200,000
Pay Fixed Rate	0.35%