Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financial Instruments
Transfers of assets between Level 1 to Level 2	$ 0	$ 0	$ 0	$ 0
Transfers of liabilities between Level 1 to Level 2	0	0	0	0
Transfers of assets between Level 2 to Level 1	0	0	0	0
Transfers of liabilities between Level 2 to Level 1	0	0	0	0
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		41,569	23,418	79,468
Total gains or (losses) (realized and unrealized)		2,946	(1,084)	(1,373)
Purchases		24,198	947	41,715
Sales		(17,871)	(1,218)	(63,910)
Settlements		(2,392)	(4,179)	(5,349)
Transfers in and/or out of Level 3				(2,101)
Balance at the end of the period	17,884	48,450	17,884	48,450
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		2,900	(1,670)	1,749
Agency mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		1,486	1,110	1,367
Total gains or (losses) (realized and unrealized)		(80)	(50)	(140)
Purchases		3		15
Sales		(1,401)	(1,060)	(1,232)
Settlements				(2)
Balance at the end of the period		8		8
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		35		4
Collateralized debt obligations
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		554	671	647
Total gains or (losses) (realized and unrealized)		(3)	(567)	(96)
Purchases				60
Sales			(104)	(60)
Balance at the end of the period		551		551
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		234		(93)
Residential mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		10,355	149	18,419
Total gains or (losses) (realized and unrealized)		331	(86)	(555)
Purchases		12,700		11,680
Sales		(11,482)	(51)	(17,329)
Settlements		(623)	(12)	(934)
Balance at the end of the period		11,281		11,281
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		37		12
Equities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		112	28	112
Total gains or (losses) (realized and unrealized)		(14)	(28)	(14)
Balance at the end of the period		98		98
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		(14)		(14)
Commercial mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		5,682	18	38,154
Total gains or (losses) (realized and unrealized)		(424)	(15)	(6,497)
Purchases		133		7,383
Sales		(1,568)	(3)	(33,058)
Settlements		(4)		(62)
Transfers in and/or out of Level 3				(2,101)
Balance at the end of the period		3,819		3,819
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		(380)		(1,322)
Other debt obligations
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		2,553		192
Total gains or (losses) (realized and unrealized)		20		10
Purchases		11,362		16,153
Sales		(3,420)		(5,848)
Settlements		(28)		(20)
Balance at the end of the period		10,487		10,487
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		3		(1)
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	20,995	19,090	20,478	18,310
Total gains or (losses) (realized and unrealized)	92	163	(338)	156
Purchases			947	800
Settlements	(3,203)		(3,203)	(13)
Balance at the end of the period	17,884	19,253	17,884	19,253
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	(1,326)	32	(1,670)	210
Derivatives
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period		1,737	964	1,696
Total gains or (losses) (realized and unrealized)		2,953		5,575
Settlements		(1,737)	(964)	(4,318)
Balance at the end of the period		2,953		2,953
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date		$ 2,953		$ 2,953