Fair Value Measurements (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Fair Value Measurements
Transfers between Level 1 and Level 2	$ 0
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period	28,416,000	25,704,000
Net gains (losses) included in: Other revenues	(100,000)	28,000
Net gains (losses) included in: Other comprehensive income (loss)	392,000	1,837,000
Purchases, sales, issues, settlements	(252,000)	(4,256,000)
Balance at end of period	28,456,000	23,313,000
Interest in a limited partnership	600,000	1,400,000	600,000
Unrealized gains or losses recognized in earnings	0	0
Investment securities:
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Purchases, sales, or issues of investment securities	0	0
Bonds:
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period	27,036,000	21,574,000
Net gains (losses) included in: Other revenues	(100,000)	33,000
Net gains (losses) included in: Other comprehensive income (loss)	432,000	1,540,000
Purchases, sales, issues, settlements	(252,000)	(3,320,000)
Balance at end of period	27,116,000	19,827,000
Corporate debt
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period	13,417,000	2,800,000
Net gains (losses) included in: Other revenues	(169,000)	3,000
Net gains (losses) included in: Other comprehensive income (loss)	510,000	184,000
Purchases, sales, issues, settlements	119,000	(2,987,000)
Balance at end of period	13,877,000
RMBS
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period	74,000	1,914,000
Net gains (losses) included in: Other revenues	(34,000)	(4,000)
Net gains (losses) included in: Other comprehensive income (loss)	25,000	(7,000)
Purchases, sales, issues, settlements		(55,000)
Balance at end of period	65,000	1,848,000
CMBS
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period	153,000	7,944,000
Net gains (losses) included in: Other revenues	(8,000)	(4,000)
Net gains (losses) included in: Other comprehensive income (loss)	6,000	601,000
Purchases, sales, issues, settlements	(149,000)	(174,000)
Balance at end of period	2,000	8,367,000
CDO/ABS
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period	13,392,000	8,916,000
Net gains (losses) included in: Other revenues	111,000	38,000
Net gains (losses) included in: Other comprehensive income (loss)	(109,000)	762,000
Purchases, sales, issues, settlements	(222,000)	(104,000)
Balance at end of period	13,172,000	9,612,000
Other long-term investments
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period	1,380,000	4,127,000
Net gains (losses) included in: Other comprehensive income (loss)	(40,000)	295,000
Purchases, sales, issues, settlements		(936,000)
Balance at end of period	1,340,000	3,486,000
Common stocks
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at beginning of period		3,000
Net gains (losses) included in: Other revenues		(5,000)
Net gains (losses) included in: Other comprehensive income (loss)		$ 2,000