Investments (Details Textual) (USD $)	3 Months Ended							3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Auction rate notes [Member]	Mar. 31, 2013 Minimum [Member]	Mar. 31, 2013 Maximum [Member]	Mar. 31, 2013 Maximum [Member] Auction rate notes [Member]	Dec. 31, 2012 Maximum [Member] Auction rate notes [Member]	Mar. 31, 2013 Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Member]	Mar. 31, 2013 Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short term investment of cash in instruments , minimum maturity period	3 months
Short-term investments, minimum maturity period	1 month
Short -term investments, maximum maturity period	2 years
Temporary impairment of these securities to accumulated other comprehensive income Net of tax								$ 28,000
Temporary impairment of these securities to accumulated other comprehensive income pre tax								44,000
Unrealized loss on short-term investments								2,100,000
Fair value of auction rate notes							4,700,000
Short-term interest rate reset dates of auction rate note securities	less than ninety days
Auction rate note securities with contractual maturities	excess of ten years
Reset period for the securities held	seven or twenty eight days
Period for principal repayments by issuer			19 years	35 years
Maximum Interest Rate					1.50%	2.50%
Comprehensive income net of tax due to auction rate notes		292,000
Comprehensive income before tax due to auction rate notes		$ 459,000