Investments (Details Textual) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Available-for-sale Securities, Gross Realized Gains	$ 1,400,000	$ 1,700,000	$ 1,500,000	$ 2,900,000
Available-for-sale Securities, Gross Realized Losses	200,000	43,000	400,000	100,000
Proceeds from Sale of Available-for-sale Securities	$ 6,000,000	$ 10,200,000	$ 6,200,000	$ 42,900,000