Common Shares (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
January 15, 2009 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	61,292
Price per Share	$ 10.85
April 15, 2009 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	7,462
Price per Share	$ 8.27
July 15, 2009 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	37,982
Price per Share	$ 8.72
October 15, 2009 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	63,471
Price per Share	$ 8.96
November 27, 2009 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	4,450,781
Price per Share	$ 9.05
January 15, 2010 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	47,385
Price per Share	$ 12.73
April 15, 2010 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	44,181
Price per Share	$ 13.75
July 15, 2010 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	50,439
Price per Share	$ 12.15
September 27, 2010 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	5,750,000
Price per Share	$ 12.25
October 15, 2010 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	48,398
Price per Share	$ 12.53
January 15, 2011 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	58,161
Price per Share	$ 11.70
April 6, 2011 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	5,750,000
Price per Share	$ 11.25
April 15, 2011 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	59,207
Price per Share	$ 11.63
July 15, 2011 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	61,224
Price per Share	$ 11.35
October 17, 2011 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	82,256
Price per Share	$ 8.46
January 17, 2012 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	12,468
Price per Share	$ 10.67
April 16, 2012 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	12,778
Price per Share	$ 10.60
July 16, 2012 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	10,767
Price per Share	$ 11.96
October 15, 2012 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	11,704
Price per Share	$ 10.24
December 1, 2012 [Member]
Sales of Common Shares
Number of Shares Issued / Repurchase	(70,040)
Price per Share	$ 10.60