Investment Securities (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investment Securities
Investment securities, sold at fair value	$ 79,900,000	$ 55,700,000	$ 45,100,000
Net realized gain recognized from sale of available for sale securities	3,163,000	2,258,000	2,893,000
Net realized gain (loss) recognized from sale of trading securities	5,300,000	1,400,000	2,900,000
Available for sale securities, sold at fair value	32,900,000	22,100,000	24,200,000
Trading securities, sold at fair value	47,000,000	33,600,000	20,900,000
Carrying amount of equity method investments	$ 4,600,000	$ 5,600,000