Marketable Securities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Marketable securities
Amortized Cost	$ 31,987,000		$ 31,987,000
Gross Unrealized Losses	(31,000)		(31,000)
Estimated Fair Value	31,956,000		31,956,000
Realized gains or losses from the sale of marketable securities	0	0	0	0
Amortized Cost
Mature in one year or less	21,749,000		21,749,000
Mature after one year through two years	10,238,000		10,238,000
Amortized cost	31,987,000		31,987,000
Estimated Fair Value
Mature in one year or less	21,734,000		21,734,000
Mature after one year through two years	10,222,000		10,222,000
Estimated Fair Value	31,956,000		31,956,000
U.S. government agency securities
Marketable securities
Amortized Cost	3,999,000		3,999,000
Gross Unrealized Losses	(3,000)		(3,000)
Estimated Fair Value	3,996,000		3,996,000
Estimated Fair Value
Estimated Fair Value	3,996,000		3,996,000
Financial
Marketable securities
Amortized Cost	21,944,000		21,944,000
Gross Unrealized Losses	(21,000)		(21,000)
Estimated Fair Value	21,923,000		21,923,000
Estimated Fair Value
Estimated Fair Value	21,923,000		21,923,000
Industrial
Marketable securities
Amortized Cost	4,017,000		4,017,000
Gross Unrealized Losses	(4,000)		(4,000)
Estimated Fair Value	4,013,000		4,013,000
Estimated Fair Value
Estimated Fair Value	4,013,000		4,013,000
Other
Marketable securities
Amortized Cost	2,027,000		2,027,000
Gross Unrealized Losses	(3,000)		(3,000)
Estimated Fair Value	2,024,000		2,024,000
Estimated Fair Value
Estimated Fair Value	$ 2,024,000		$ 2,024,000