Dividends (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended			0 Months Ended												12 Months Ended							12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 14, 2012 Ordinary Shares	Sep. 14, 2012 Ordinary Shares	Jun. 15, 2012 Ordinary Shares	Mar. 15, 2012 Ordinary Shares	Dec. 15, 2011 Ordinary Shares	Sep. 15, 2011 Ordinary Shares	Jun. 15, 2011 Ordinary Shares	Mar. 15, 2011 Ordinary Shares	Dec. 15, 2010 Ordinary Shares	Sep. 15, 2010 Ordinary Shares	Jun. 15, 2010 Ordinary Shares	Mar. 15, 2010 Ordinary Shares	Dec. 31, 2012 Series C preference ordinary shares	Dec. 31, 2011 Series C preference ordinary shares	Dec. 31, 2010 Series C preference ordinary shares	Dec. 31, 2012 Series D preference ordinary shares	Dec. 31, 2011 Series D preference ordinary shares	Dec. 31, 2010 Series D preference ordinary shares	Oct. 26, 2012 Series D preference ordinary shares	Dec. 31, 2012 Series E preference ordinary shares	Dec. 31, 2011 Series E preference ordinary shares	Dec. 31, 2010 Series E preference ordinary shares
Dividends Paid [Line Items]
Dividends per share paid on ordinary shares	$ 0.44	$ 0.44	$ 0.40	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.10	$ 0.10	$ 0.10	$ 0.10
Dividends declared and payable per share																						$ 8.8173
Dividends on preference ordinary shares	$ 0	$ 0	$ 34,694													$ 0	$ 5,300	$ 7,900	$ 14,000	$ 0	$ 0		$ 65,100	$ 66,200	$ 69,900