Fair value measurements (Details 1) (USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance of other assets and other liabilities	$ 16,147	$ 8,171	$ 2,244	$ (80)
Total gains (losses) realized/ unrealized;
Included In Earnings of other assets and other liabilities	22,800	29,828	43,244	47,850
Transfer in and/or out of Level 3 of other assets and other liabilities	(25,776)	(17,156)	(32,317)	(26,927)
Ending Balance of other assets and other liabilities	13,171	20,843	13,171	20,843
Changes in unrealized gains (losses) included in earnings related to other assets and other liabilities still held at end of period	10,252	20,097	13,139	20,598
Privately issued residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,391,878	1,661,341	1,435,561	2,064,904
Total gains (losses) realized/ unrealized;
Included in earnings	(24,530)	(7,896)	(32,071)	(34,343)
Included in other comprehensive income	38,471	40,794	99,556	115,248
Settlements	(99,617)	(99,206)	(196,844)	(192,528)
Transfer in and/or out of Level 3				(355,248)
Ending Balance	1,306,202	1,598,033	1,306,202	1,598,033
Changes in unrealized gains (losses) included in earnings related to assets still held at end of period	(24,530)	(7,896)	(32,071)	(34,343)
Privately issued commercial [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	20,467	25,125	22,407	25,166
Total gains (losses) realized/ unrealized;
Included in other comprehensive income	(1,400)	4,021	(1,482)	6,094
Settlements	(1,834)	(2,503)	(3,692)	(4,617)
Ending Balance	17,233	26,643	17,233	26,643
Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	114,265	125,755	110,756	115,346
Total gains (losses) realized/ unrealized;
Included in earnings		(2,491)		(2,846)
Included in other comprehensive income	3,372	(5,088)	7,206	5,807
Purchases	50,790		50,790
Sales	(105,643)		(105,643)
Settlements	(1,183)	(136)	(1,508)	(267)
Ending Balance	61,601	118,040	61,601	118,040
Changes in unrealized gains (losses) included in earnings related to assets still held at end of period		(2,491)		(2,846)
Other Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		455		420
Total gains (losses) realized/ unrealized;
Included in other comprehensive income				35
Transfer in and/or out of Level 3		$ (455)		$ (455)

Fair value measurement with unobservable inputs reconciliation recurring Basis asset purchases.

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis asset sales.

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- Definition

Changes in unrealized gains (losses) included in earnings related to assets still held at end of period

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis other asset and other liability still held gain loss in earnings.

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- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Other Asset And Other Liability Value.

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- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Other Assets and other liabilities Gain Loss Included In Earnings.

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- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Other Assets and other liabilities Transfers Net.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1)

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1)

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- Definition

This element represents purchases, sales, issuances, and settlements (net) which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(2)

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- Definition

This element represents [net] transfers in to and out of assets measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(3)

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c

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