Condensed Statements Of Income (Parenthetical) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Distributions declared per share	$ 3.00	[1]	$ 3.00	[2]	$ 5.25	[3]	$ 5.25	[4]
3 Months Ended Quarter 2, 2012 [Member]
Distributions declared per share	$ 3.00
Dividends declared date					Jun. 06, 2012
Dividends payable date					Jul. 31, 2012
3 Months Ended Quarter 2, 2011 [Member]
Distributions declared per share			$ 3.00
Dividends declared date					Jun. 10, 2011
Dividends payable date					Jul. 29, 2011
6 Months Ended Quarter 2, 2012, Dividend 1 [Member]
Distributions declared per share					$ 2.25
Dividends declared date					Mar. 09, 2012
Dividends payable date					Apr. 30, 2012
6 Months Ended Quarter 2, 2012, Dividend 2 [Member]
Distributions declared per share					$ 3.00
Dividends declared date					Jun. 06, 2012
Dividends payable date					Jul. 31, 2012
6 Months Ended Quarter 2, 2011, Dividend 1 [Member]
Distributions declared per share							$ 2.25
Dividends declared date					Mar. 10, 2011
Dividends payable date					Apr. 29, 2011
6 Months Ended Quarter 2, 2011, Dividend 2 [Member]
Distributions declared per share							$ 3.00
Dividends declared date					Jun. 10, 2011
Dividends payable date					Jul. 29, 2011

[1] $3.00 declared 6/6/2012 payable 7/31/2012

[2] $3.00 declared 6/10/2011 paid 7/29/2011

[3] $2.25 declared 3/9/2012 paid 4/30/2012 plus $3.00 declared 6/6/2012 payable 7/31/2012

[4] $2.25 declared 3/10/2011 paid 4/29/2011 plus $3.00 declared 6/10/2011 paid 7/29/2011