Fair Value Measurements (Details Textual) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Fair Value Measurements (Textual) [Abstract]
Net unrealized gains	$ 879,000	$ 689,000	$ 4,217,000	$ 3,010,000