Debt Security Investments (Details Textual) (USD $)	1 Months Ended				3 Months Ended	12 Months Ended
	Feb. 28, 2013	Dec. 31, 2012	Oct. 31, 2012	Aug. 31, 2012	Sep. 30, 2012	Dec. 31, 2012 Security	Dec. 31, 2011
Debt Security Investments (Additional Textual) [Abstract]
U.S. treasury securities, to available for sale					$ 72,500,000
Special cash dividend declared per share	$ 0.15		$ 10.00	$ 10.00	$ 10.00	$ 10.15
Debt security investments matured amount						66,328,000
Debt security investments sold						6,200,000
Proceeds from sale of held to maturity debt security investments						7,628,000
Proceeds from maturity of held to maturity debt security investments						35,967,000
Cash dividends declared		(1,300,000)	(88,800,000)			(90,439,000)
Fair value of investment		3,499,000				3,499,000
Debt security investments were outstanding for 12 months or more						0
Amortized Cost		3,486,000				3,486,000
Unrealized gains on available for sale securities		8,000				8,000
Impairments on the debt security investments						0	0
Senior Notes [Member]
Debt Security Investments (Textual) [Abstract]
Redemption of remaining senior notes, amount						$ 61,800,000
Redemption of remaining senior notes, percentage		8.625%				8.625%