Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended											3 Months Ended			3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Agency mortgage-backed securities	Mar. 31, 2012 Agency mortgage-backed securities	Mar. 31, 2013 Collateralized debt obligations	Mar. 31, 2012 Collateralized debt obligations	Mar. 31, 2013 Residential mortgage-backed securities	Mar. 31, 2012 Residential mortgage-backed securities	Mar. 31, 2012 Equity securities	Mar. 31, 2013 Equity securities	Dec. 31, 2012 Equity securities	Mar. 31, 2012 Commercial mortgage-backed securities	Mar. 31, 2013 Commercial mortgage-backed securities	Dec. 31, 2012 Commercial mortgage-backed securities	Mar. 31, 2012 Other debt obligations	Mar. 31, 2012 Preferred stock	Mar. 31, 2013 Investments	Mar. 31, 2012 Investments	Mar. 31, 2013 Derivatives	Mar. 31, 2012 Derivatives
Financial Instruments
Transfers of assets between Level 1 to Level 2	$ 0	$ 0
Transfers of liabilities between Level 1 to Level 2	0	0
Transfers of assets between Level 2 to Level 1	0	0
Transfers of liabilities between Level 2 to Level 1	0	0
Changes in the company's Level 3 financial instruments
Balance at the beginning of the period	23,418	79,468	1,110	1,367	671	647	149	18,419	112	28	28	38,154	18	18	192	571	20,478	18,310	964	1,696
Total gains or (losses) (realized and unrealized)	119	(3,066)	(45)	(68)	(12)	(62)	4	(548)	(9)			(3,505)			3	106	172	132		885
Purchases	947	45,605		295				26,529				14,845			3,254	682	947
Sales	(1,110)	(42,041)	(1,060)	(1,232)			(50)	(16,156)				(20,163)			(3,131)	(1,359)
Settlements	(976)	(2,514)					(12)	(682)				(134)						(2)	(964)	(1,696)
Transfers in and/or out of Level 3		(2,306)						(959)				(1,347)
Balance at the end of the period	22,398	75,146	5	362	659	585	91	26,603	103	28	28	27,850	18	18	318		21,597	18,440		885
Changes in unrealized gains/(losses) on Level 3 assets still held at the reporting date	$ 176	$ (1,974)		$ (60)	$ (12)	$ (61)		$ (32)	$ (10)			$ (3,019)			$ (2)		$ 188	$ 325		$ 885