Subsequent Events (Details) (Amended And Restated Credit Facility [Member], USD $) In Billions, unless otherwise specified	1 Months Ended
	Mar. 19, 2012
Line of Credit Facility [Line Items]
Line of credit revolving facility initial amount	$ 1.3
Revolving credit facility potential increase	$ 1.6
Expiry date	Mar. 19, 2017
Line of credit facility interest rate above federal funds rate	0.50%
Line of credit facility interest rate above one month LIBOR rate	1.00%
Maximum [Member]
Line of Credit Facility [Line Items]
Rate of interest	0.85%
Line of credit facility interest rate above Eurocurrency rate	1.85%
Minimum [Member]
Line of Credit Facility [Line Items]
Rate of interest	0.175%
Line of credit facility interest rate above Eurocurrency rate	1.175%