Marketable Securities (Schedule Of Marketable Securities) (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Marketable Securities - Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	$ 7,790,000	$ 11,458,000
Unrealized Gains	11,000	15,000
Unrealized Losses		(35,000)
Fair Value	7,801,000	11,438,000
Marketable Securities - Short-Term [Member] | US States Government And Agency Obligations [Member]
Gain (Loss) on Investments [Line Items]
Cost	5,965,000	7,358,000
Unrealized Gains	9,000	10,000
Unrealized Losses		(35,000)
Fair Value	5,974,000	7,333,000
Marketable Securities - Short-Term [Member] | Corporate Debt Securities And Certificates Of Deposit [Member]
Gain (Loss) on Investments [Line Items]
Cost	1,825,000	4,100,000
Unrealized Gains	2,000	5,000
Fair Value	1,827,000	4,105,000
Marketable Securities - Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	11,421,000	10,432,000
Unrealized Gains	31,000	27,000
Unrealized Losses	(7,000)	(24,000)
Fair Value	11,445,000	10,435,000
Marketable Securities - Long-Term [Member] | US States Government And Agency Obligations [Member]
Gain (Loss) on Investments [Line Items]
Cost	6,752,000	9,033,000
Unrealized Gains	12,000	23,000
Unrealized Losses	(2,000)	(23,000)
Fair Value	6,762,000	9,033,000
Marketable Securities - Long-Term [Member] | Corporate Debt Securities And Certificates Of Deposit [Member]
Gain (Loss) on Investments [Line Items]
Cost	3,004,000	1,192,000
Unrealized Gains	4,000	4,000
Unrealized Losses	(5,000)	(1,000)
Fair Value	3,003,000	1,195,000
Marketable Securities - Long-Term [Member] | Asset-backed Securities [Member]
Gain (Loss) on Investments [Line Items]
Cost	1,623,000	165,000
Unrealized Gains	1,000
Fair Value	1,624,000	165,000
Marketable Securities - Long-Term [Member] | Equity Security [Member]
Gain (Loss) on Investments [Line Items]
Cost	42,000	42,000
Unrealized Gains	14,000
Fair Value	$ 56,000	$ 42,000