Noncontrolling interests (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Noncontrolling Interest [Line Items]
Total assets	$ 23,138,207,000		$ 23,138,207,000		$ 22,980,432,000
Total liabilities	16,514,031,000		16,514,031,000		16,046,936,000
Movement In Minority Interest [Roll Forward]
Beginning balance			0
Net income attributable to noncontrollong interests	4,112,000	0	5,296,000	0
Ending balance	52,489,000		52,489,000
[LorenzReMember]
Noncontrolling Interest [Line Items]
Interest Ownership Percentage By Parent	50.00%		50.00%
Noncontrolling Interest Ownership Percentage By Noncontrolling Owners	50.00%		50.00%
Preferred Stock Value Issued Of Subsidiary	75,000,000		75,000,000
Sale of shares to noncontrolling interests	10,500,000		47,193,000
Total assets	100,900,000		100,900,000
Total liabilities	18,900,000		18,900,000
Movement In Minority Interest [Roll Forward]
Beginning balance			0
Sale of shares to noncontrolling interests	10,500,000		47,193,000
Net income attributable to noncontrollong interests			5,296,000
Ending balance	$ 52,489,000		$ 52,489,000