Financial Instruments (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Financial Instruments
Transfers of financial instruments between Level 1 and 2	$ 0
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	79,468,000	128,203,000
Total gains or (losses) (realized and unrealized)	673,000	31,181,000
Purchases	18,655,000	121,126,000
Sales	(66,413,000)	(189,353,000)
Settlements	(7,969,000)	(11,689,000)
Transfers in and/or out of Level 3	(996,000)
Balance at the end of the period	23,418,000	79,468,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	2,449,000	(7,108,000)
Agency mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	1,367,000	806,000
Total gains or (losses) (realized and unrealized)	(350,000)	(64,000)
Purchases	222,000	1,608,000
Sales	(1,232,000)	(982,000)
Settlements	(2,000)	(1,000)
Transfers in and/or out of Level 3	1,105,000
Balance at the end of the period	1,110,000	1,367,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	(181,000)	(148,000)
Collateralized debt obligations
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	647,000	23,235,000
Total gains or (losses) (realized and unrealized)	24,000	18,624,000
Purchases	61,000	5,488,000
Sales	(61,000)	(46,175,000)
Settlements		(525,000)
Balance at the end of the period	671,000	647,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	28,000	63,000
Residential mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	18,419,000	33,604,000
Total gains or (losses) (realized and unrealized)	(623,000)	(625,000)
Purchases	303,000	28,250,000
Sales	(17,329,000)	(39,610,000)
Settlements	(621,000)	(3,200,000)
Balance at the end of the period	149,000	18,419,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	14,000	86,000
Equity securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	112,000	60,000
Total gains or (losses) (realized and unrealized)	(84,000)	52,000
Balance at the end of the period	28,000	112,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	(85,000)	(108,000)
Commercial mortgage-backed securities
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	38,154,000	46,571,000
Total gains or (losses) (realized and unrealized)	(6,938,000)	4,745,000
Purchases	8,393,000	79,432,000
Sales	(37,432,000)	(92,425,000)
Settlements	(58,000)	(169,000)
Transfers in and/or out of Level 3	(2,101,000)
Balance at the end of the period	18,000	38,154,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	(58,000)	(10,820,000)
Other debt obligations
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	192,000	5,843,000
Total gains or (losses) (realized and unrealized)		(4,000)
Purchases	3,784,000	3,847,000
Sales	(3,976,000)	(9,431,000)
Settlements		(63,000)
Balance at the end of the period		192,000
Preferred stock
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	571,000
Total gains or (losses) (realized and unrealized)	870,000
Purchases	4,942,000	1,301,000
Sales	(6,383,000)	(730,000)
Balance at the end of the period		571,000
Investments
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	18,310,000	18,084,000
Total gains or (losses) (realized and unrealized)	1,235,000	2,149,000
Purchases	950,000	1,200,000
Settlements	(17,000)	(3,123,000)
Balance at the end of the period	20,478,000	18,310,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	1,767,000	2,123,000
Derivatives
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	1,696,000
Total gains or (losses) (realized and unrealized)	6,539,000	6,304,000
Settlements	(7,271,000)	(4,608,000)
Balance at the end of the period	964,000	1,696,000
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	$ 964,000	$ 1,696,000