Marketable Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of the gross unrealized losses and market value of available-for-sale securities with unrealized losses
Available for sale securities, Less Than 12 Months, Market Value	$ 8,976	$ 27,146
Available for sale securities, Less Than 12 Months, Unrealized Losses	15	43
Available for sale securities, 12 Months or Greater, Market Value	8,926	8,970
Available for sale securities, 12 Months or Greater, Unrealized Losses	2,074	2,030
State and municipal bonds [Member]
Summary of the gross unrealized losses and market value of available-for-sale securities with unrealized losses
Available for sale securities, Less Than 12 Months, Market Value		9,430
Available for sale securities, Less Than 12 Months, Unrealized Losses		14
Available for sale securities, 12 Months or Greater, Market Value
Available for sale securities, 12 Months or Greater, Unrealized Losses
Federal agency and corporate obligations [Member]
Summary of the gross unrealized losses and market value of available-for-sale securities with unrealized losses
Available for sale securities, Less Than 12 Months, Market Value	8,976	17,716
Available for sale securities, Less Than 12 Months, Unrealized Losses	15	29
ARS [Member]
Summary of the gross unrealized losses and market value of available-for-sale securities with unrealized losses
Available for sale securities, 12 Months or Greater, Market Value	8,926	8,970
Available for sale securities, 12 Months or Greater, Unrealized Losses	$ 2,074	$ 2,030