Derivative Financial Instruments Outstanding Interest Rate Swap Agreements (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Derivatives [Line Items]
Gain/loss reclassified from accumulated other comprehensive into earnings, ineffective portion	$ 0
Loss reclassified from accumulated OCI into income (interest expense), effective portion, gross	1,200,000	1,900,000
Interest rate swap agreements [Member]
Derivatives [Line Items]
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred		(1,800,000)
Interest Rate Swap 8 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	120,000,000	120,000,000
Derivative, fixed interest rate	3.88%	3.88%
Interest Rate Swap 1 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,450,000,000	1,450,000,000
Derivative, fixed interest rate	0.25%	0.25%
Interest Rate Swap 1 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,350,000,000	1,350,000,000
Derivative, fixed interest rate	0.25%	0.25%
Interest Rate Swap 1 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,300,000,000	1,300,000,000
Derivative, fixed interest rate	0.25%	0.25%
Interest Rate Swap 1 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,250,000,000	1,250,000,000
Derivative, fixed interest rate	0.25%	0.25%
Interest Rate Swap 2 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,350,000,000	1,350,000,000
Derivative, fixed interest rate	0.35%	0.35%
Interest Rate Swap 2 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,300,000,000	1,300,000,000
Derivative, fixed interest rate	0.35%	0.35%
Interest Rate Swap 2 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,250,000,000	1,250,000,000
Derivative, fixed interest rate	0.35%	0.35%
Interest Rate Swap 2 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,200,000,000	1,200,000,000
Derivative, fixed interest rate	0.35%	0.35%
Interest Rate Swap 3 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,150,000,000	1,150,000,000
Derivative, fixed interest rate	0.54%	0.54%
Interest Rate Swap 3 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,100,000,000	1,100,000,000
Derivative, fixed interest rate	0.54%	0.54%
Interest Rate Swap 3 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,050,000,000	1,050,000,000
Derivative, fixed interest rate	0.54%	0.54%
Interest Rate Swap 3 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Derivative, notional amount	1,000,000,000	1,000,000,000
Derivative, fixed interest rate	0.54%	0.54%
Interest Rate Swap 4 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	350,000,000	350,000,000
Derivative, fixed interest rate	0.93%	0.93%
Interest Rate Swap 5 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	100,000,000	100,000,000
Derivative, fixed interest rate	2.79%	2.79%
Interest Rate Swap 6 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	100,000,000	100,000,000
Derivative, fixed interest rate	2.79%	2.79%
Interest Rate Swap 7 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, notional amount	$ 100,000,000	$ 100,000,000
Derivative, fixed interest rate	2.80%	2.80%
1-month LIBOR [Member] | Interest Rate Swap 8 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 1 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 1 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 1 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 1 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 2 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 2 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 2 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 2 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 3 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 3 [Member] | Notional Period 2 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 3 [Member] | Notional Period 3 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 3 [Member] | Notional Period 4 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
1-month LIBOR [Member] | Interest Rate Swap 4 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		1-month LIBOR
3-month LIBOR [Member] | Interest Rate Swap 5 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		3-month LIBOR
3-month LIBOR [Member] | Interest Rate Swap 6 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		3-month LIBOR
3-month LIBOR [Member] | Interest Rate Swap 7 [Member] | Notional Period 1 [Member]
Derivatives [Line Items]
Derivative, description of variable rate basis		3-month LIBOR