Marketable Investments (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended									9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Minimum [Member]	Sep. 30, 2011 Minimum [Member]	Sep. 30, 2012 Maximum [Member]	Sep. 30, 2011 Maximum [Member]	Sep. 30, 2012 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Dec. 31, 2011 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Sep. 30, 2012 Federal agency and corporate obligations [Member]	Dec. 31, 2011 Federal agency and corporate obligations [Member]	Sep. 30, 2012 ARS [Member] Level 3 [Member]
Marketable Investments (Textual) [Abstract]
Cash and cash equivalents								$ 10.1	$ 1.0
Original maturities	90 days
Intervals for each security		7 days		35 days
Interest rates on securities ranged		0.11%	0.12%	0.46%	0.60%
Weighted average interest rate										0.30%
Weighted average discount rate										2.84%
Weighted average holding period										5 years
Unrealized loss recorded in other comprehensive loss						$ 1.2	$ 1.4