Derivative Financial Instruments Interest Rate Risk Management (Details) (USD $)	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012	Oct. 02, 2008 Interest Rate Swap [Member]	Dec. 31, 2012 Interest Rate Swap [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 1 [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 1 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 2 [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 2 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 3 [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 3 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 4 [Member]	Dec. 31, 2012 Interest Rate Swap 1 [Member] Notional Period 4 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 1 [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 1 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 2 [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 2 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 3 [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 3 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 4 [Member]	Dec. 31, 2012 Interest Rate Swap 2 [Member] Notional Period 4 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 1 [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 1 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 2 [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 2 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 3 [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 3 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 4 [Member]	Dec. 31, 2012 Interest Rate Swap 3 [Member] Notional Period 4 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Interest Rate Swap 4 [Member] Notional Period 1 [Member]	Dec. 31, 2012 Interest Rate Swap 4 [Member] Notional Period 1 [Member] 1-month LIBOR [Member]	Dec. 31, 2012 Forward Starting Interest Rate Swap 1 [Member]	Dec. 31, 2012 Forward Starting Interest Rate Swap 1 [Member] 3-month LIBOR [Member]
Notional Amount of Interest Rate Derivatives		$ 120,000,000		$ 1,450,000,000		$ 1,350,000,000		$ 1,300,000,000		$ 1,250,000,000		$ 1,350,000,000		$ 1,300,000,000		$ 1,250,000,000		$ 1,200,000,000		$ 1,150,000,000		$ 1,100,000,000		$ 1,050,000,000		$ 1,000,000,000		$ 350,000,000		$ 300,000,000
Derivative, Fixed Interest Rate		3.88%		0.25%		0.25%		0.25%		0.25%		0.35%		0.35%		0.35%		0.35%		0.54%		0.54%		0.54%		0.54%		0.93%		2.79%
Derivative, description of variable rate basis			one-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		three-month LIBOR
Probable Company issued fixed rate debt	300,000,000
Probable future borrowings	300,000,000
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$ 0