Condensed Statements Of Income (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Distributions declared per share	$ 2.25	[1]	$ 2.25	[2]
Three Months Ended Quarter 1, 2013 [Member]
Distributions declared per share	$ 2.25
Dividends declared date	Mar. 08, 2013
Dividends payable date	Apr. 30, 2013
Three Months Ended Quarter 1, 2012 [Member]
Distributions declared per share			$ 2.25
Dividends declared date	Mar. 09, 2012
Dividends payable date	Apr. 30, 2012

[1] $2.25 declared 3/8/2013 payable 4/30/2013

[2] $2.25 declared 3/9/2012 paid 4/30/2012