Noncontrolling interests (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Noncontrolling Interest [Line Items]
Total assets	$ 22,570,580,000		$ 22,570,580,000		$ 22,980,432,000
Total liabilities	16,155,304,000		16,155,304,000		16,046,936,000
Movement In Minority Interest [Roll Forward]
Beginning balance			0
Net income attributable to noncontrollong interests	1,183,000	0	1,183,000	0
Ending balance	48,319,000		48,319,000
[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		47,136,000
Total assets	96,400,000		96,400,000
Total liabilities	21,100,000		21,100,000
Movement In Minority Interest [Roll Forward]
Beginning balance			0
Sale of shares to noncontrolling interests	10,500,000		47,136,000
Net income attributable to noncontrollong interests			1,183,000
Ending balance	$ 48,319,000		$ 48,319,000