Marketable Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
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	$ 15,968	$ 71,725
Available for sale securities, Less Than 12 Months, Unrealized Losses	9	322
Available for sale securities, 12 Months or Greater, Market Value	9,789	12,715
Available for sale securities, 12 Months or Greater, Unrealized Losses	1,211	1,460
State and municipal 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	9,531	2,763
Available for sale securities, Less Than 12 Months, Unrealized Losses	5	9
Available for sale securities, 12 Months or Greater, Market Value		1,107
Available for sale securities, 12 Months or Greater, Unrealized Losses		3
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	6,437	68,962
Available for sale securities, Less Than 12 Months, Unrealized Losses	4	313
Available for sale securities, 12 Months or Greater, Market Value		2,043
Available for sale securities, 12 Months or Greater, Unrealized Losses		22
ARS [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
Available for sale securities, Less Than 12 Months, Unrealized Losses
Available for sale securities, 12 Months or Greater, Market Value	9,789	9,565
Available for sale securities, 12 Months or Greater, Unrealized Losses	$ 1,211	$ 1,435