Investment securities (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 267,473	$ 322,719	$ 285,399	$ 327,912
Additions for credit losses not previously recognized	16,173	26,530	27,659	42,571
Reductions for increases in cash flows		(4,881)		(5,020)
Reductions For Realized Losses	(19,449)	(46,227)	(48,861)	(67,322)
Ending balance	$ 264,197	$ 298,141	$ 264,197	$ 298,141