Equity (Details Textuals) (USD $) In Thousands, except Per Share data	1 Months Ended	3 Months Ended	6 Months Ended
Aug. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Jun. 30, 2011	Jun. 30, 2010	Jun. 17, 2011	Mar. 16, 2011	Jun. 18, 2010	May 19, 2010
Equity (Textuals) [Abstract]
Dividends declared per common share	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.18	$ 0.18	$ 0.18	$ 0.42	$ 0.36
Total dividend paid										$ 23,976	$ 23,897	$ 20,209	$ 20,046

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

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Balance Type:	na
Period Type:	duration