Marketable Securities (Schedule Of Marketable Securities) (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Marketable Securities - Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	$ 11,793,000	$ 11,458,000
Unrealized Gains	17,000	15,000
Unrealized Losses	(3,000)	(35,000)
Fair Value	11,807,000	11,438,000
Marketable Securities - Short-Term [Member] | US States Government And Agency Obligations [Member]
Gain (Loss) on Investments [Line Items]
Cost	7,577,000	7,358,000
Unrealized Gains	13,000	10,000
Unrealized Losses	(3,000)	(35,000)
Fair Value	7,587,000	7,333,000
Marketable Securities - Short-Term [Member] | Corporate Debt Securities And Certificates Of Deposit [Member]
Gain (Loss) on Investments [Line Items]
Cost	4,216,000	4,100,000
Unrealized Gains	4,000	5,000
Fair Value	4,220,000	4,105,000
Marketable Securities - Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	10,139,000	10,432,000
Unrealized Gains	27,000	27,000
Unrealized Losses	(1,000)	(24,000)
Fair Value	10,165,000	10,435,000
Marketable Securities - Long-Term [Member] | US States Government And Agency Obligations [Member]
Gain (Loss) on Investments [Line Items]
Cost	7,964,000	9,033,000
Unrealized Gains	20,000	23,000
Unrealized Losses		(23,000)
Fair Value	7,984,000	9,033,000
Marketable Securities - Long-Term [Member] | Corporate Debt Securities And Certificates Of Deposit [Member]
Gain (Loss) on Investments [Line Items]
Cost	1,504,000	1,192,000
Unrealized Gains	4,000	4,000
Unrealized Losses	(1,000)	(1,000)
Fair Value	1,507,000	1,195,000
Marketable Securities - Long-Term [Member] | Asset-backed Securities [Member]
Gain (Loss) on Investments [Line Items]
Cost	629,000	165,000
Fair Value	629,000	165,000
Marketable Securities - Long-Term [Member] | Equity Security [Member]
Gain (Loss) on Investments [Line Items]
Cost	42,000	42,000
Unrealized Gains	3,000
Fair Value	$ 45,000	$ 42,000