Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	$ 41,569	$ 125,719	$ 79,468	$ 128,203
Total gains or (losses) (realized and unrealized)	2,946	98	(1,373)	27,470
Purchases	24,198	60,135	41,715	144,204
Sales	(17,871)	(77,527)	(63,910)	(180,841)
Settlements	(2,392)	(4,614)	(5,349)	(8,007)
Transfers in and/or out of Level 3			(2,101)	(7,218)
Balance at the end of the period	48,450	103,811	48,450	103,811
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	2,900	1,441	1,749	(1,600)
Commercial mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	5,682	56,359	38,154	46,571
Total gains or (losses) (realized and unrealized)	(424)	(6,258)	(6,497)	8,828
Purchases	133		7,383	67,742
Sales	(1,568)	(22,353)	(33,058)	(91,668)
Settlements	(4)	(32)	(62)	(107)
Transfers in and/or out of Level 3			(2,101)	(3,650)
Balance at the end of the period	3,819	27,716	3,819	27,716
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	(380)	(4,355)	(1,322)	(6,889)
Residential mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	10,355	27,193	18,419	33,604
Total gains or (losses) (realized and unrealized)	331	75	(555)	(79)
Purchases	12,700	28,568	11,680	32,923
Sales	(11,482)	(21,289)	(17,329)	(30,564)
Settlements	(623)	(1,652)	(934)	(2,989)
Balance at the end of the period	11,281	32,895	11,281	32,895
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	37	(379)	12	(379)
Other debt obligations
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	2,553	15,998	192	5,843
Total gains or (losses) (realized and unrealized)	20	(94)	10	(14)
Purchases	11,362	27,464	16,153	32,005
Sales	(3,420)	(23,299)	(5,848)	(18,765)
Settlements	(28)	(1,160)	(20)	(160)
Balance at the end of the period	10,487	18,909	10,487	18,909
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	3	(3)	(1)	54
Agency mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	1,486	8,013	1,367	806
Total gains or (losses) (realized and unrealized)	(80)	(95)	(140)	(147)
Purchases	3	2,839	15	1,111
Sales	(1,401)	(9,709)	(1,232)	(722)
Settlements			(2)
Balance at the end of the period	8	1,048	8	1,048
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	35	(124)	4	(187)
Collateralized debt obligations
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	554	1,424	647	23,235
Total gains or (losses) (realized and unrealized)	(3)	99	(96)	11,570
Purchases			60	9,056
Sales		(877)	(60)	(39,122)
Settlements				(525)
Transfers in and/or out of Level 3				(3,568)
Balance at the end of the period	551	646	551	646
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	234	136	(93)	61
Equity securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	112	60	112	60
Total gains or (losses) (realized and unrealized)	(14)	165	(14)	165
Balance at the end of the period	98	225	98	225
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	(14)	(55)	(14)	(55)
Preferred stock
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period			571
Total gains or (losses) (realized and unrealized)			188
Purchases			5,624
Sales			(6,383)
Investments
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	19,090	16,098	18,310	18,084
Total gains or (losses) (realized and unrealized)	163	2,857	156	2,539
Purchases		1,264	800	1,367
Settlements		(1,196)	(13)	(2,967)
Balance at the end of the period	19,253	19,023	19,253	19,023
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	32	2,872	210	2,446
Derivatives
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	1,737	574	1,696
Total gains or (losses) (realized and unrealized)	2,953	3,349	5,575	4,608
Settlements	(1,737)	(574)	(4,318)	(1,259)
Balance at the end of the period	2,953	3,349	2,953	3,349
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	$ 2,953	$ 3,349	$ 2,953	$ 3,349