Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity Schedule of Dividends Declared (Details)

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Stockholders' Equity Schedule of Dividends Declared (Details) (USD $)
 3 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2010
Sep. 30, 2010
Jun. 30, 2010
Mar. 31, 2010
Dec. 31, 2009
Dividends Payable [Line Items]                            
Dividends Payable, Date Declared Mar. 18, 2013 Dec. 17, 2012 Sep. 12, 2012 Jun. 12, 2012 Mar. 14, 2012 Dec. 14, 2011 Sep. 14, 2011 Jun. 14, 2011 Mar. 02, 2011 Dec. 08, 2010 Sep. 13, 2010 Jun. 14, 2010 Mar. 12, 2010 Dec. 21, 2009
Dividends Payable, Date of Record Apr. 02, 2013 Dec. 31, 2012 Sep. 24, 2012 Jun. 22, 2012 Mar. 26, 2012 Dec. 27, 2011 Sep. 26, 2011 Jun. 24, 2011 Mar. 14, 2011 Dec. 17, 2010 Sep. 30, 2010 Jun. 30, 2010 Mar. 31, 2010 Dec. 31, 2009
Dividends Payable, Date to be Paid Apr. 24, 2013 Jan. 18, 2013 Oct. 22, 2012 Jul. 20, 2012 Apr. 20, 2012 Jan. 20, 2012 Oct. 20, 2011 Jul. 20, 2011 Apr. 14, 2011 Jan. 20, 2011 Oct. 21, 2010 Jul. 22, 2010 Apr. 23, 2010 Jan. 26, 2010
Common Stock, Dividends, Per Share, Declared $ 0.32 $ 0.55 $ 0.36 $ 0.40 $ 0.40 $ 0.40 $ 0.40 $ 0.40 $ 0.40 $ 0.40 $ 0.39 $ 0.33 $ 0.36 $ 0.26