Cash and Cash Equivalents and Marketable Securities (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Available-for-sale Securities [Abstract]
Amortized Cost	$ 87,958,000	$ 85,441,000
Gross Unrealized Gains	143,000	138,000
Gross Unrealized Losses	(8,000)	(7,000)
Fair Market Value	88,093,000	85,572,000
Unrealized loss positions for more than 12 months	0
Estimated fair value of marketable investments and long-term investments classified by contractual maturity date [Abstract]
Due in less than one year	39,455,000
Due in 1 to 3 years	34,565,000
Due in 3 to 10 years	0
Due in greater than 10 years	0
Total	74,020,000
U.S. government notes [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	4,001,000	4,005,000
Gross Unrealized Gains	5,000	4,000
Gross Unrealized Losses	0	0
Fair Market Value	4,006,000	4,009,000
U.S. government agencies [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	32,249,000	24,910,000
Gross Unrealized Gains	44,000	48,000
Gross Unrealized Losses	(1,000)	0
Fair Market Value	32,292,000	24,958,000
Municipal securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	5,467,000	4,184,000
Gross Unrealized Gains	17,000	23,000
Gross Unrealized Losses	(2,000)	(1,000)
Fair Market Value	5,482,000	4,206,000
Commercial paper [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	10,958,000	10,515,000
Gross Unrealized Gains	7,000	4,000
Gross Unrealized Losses	(1,000)	0
Fair Market Value	10,964,000	10,519,000
Corporate debt securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	18,011,000	18,281,000
Gross Unrealized Gains	70,000	59,000
Gross Unrealized Losses	(4,000)	(6,000)
Fair Market Value	18,077,000	18,334,000
Cash [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	1,740,000	2,198,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	1,740,000	2,198,000
Money Market Funds [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	12,333,000	17,438,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	12,333,000	17,348,000
Commercial Paper [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	3,199,000	4,000,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	3,199,000	4,000,000
Cash and Cash Equivalents [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	17,272,000	23,546,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	17,272,000	23,546,000
Marketable Securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	70,686,000	61,895,000
Gross Unrealized Gains	143,000	138,000
Gross Unrealized Losses	(8,000)	(7,000)
Fair Market Value	$ 70,821,000	$ 62,026,000