Short-Term Investments (Details) (USD $)	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Remaing maturity date in days for marketable securites to be classified as short-term investments	90 days
Average remaining contractual maturity of marketable securities		1 year
Amortized Cost	$ 81,935,000	$ 85,226,000
Cash and Cash Equivalents, Amortized Cost	72,237,000	75,326,000	62,920,000	35,987,000
Cash and Cash equivalents, Amortized Cost	81,935,000	85,226,000
Gross Unrealized Gains	0	1,000
Gross Unrealized Losses	(3,000)	(4,000)
Fair Value	81,932,000	85,223,000
Cash equivalents	11,000,000	10,300,000
Obligations of U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,379,000	6,219,000
Gross Unrealized Gains	0	1,000
Gross Unrealized Losses	(3,000)	(1,000)
Fair Value	7,376,000	6,219,000
Obligations of U.S. corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,995,000	2,633,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(3,000)
Fair Value	1,995,000	2,630,000
Foreign Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	324,000	1,048,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	324,000	1,048,000
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		275,000
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		275,000
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,039,000	10,035,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	11,039,000	10,035,000
Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		75,326,000
Cash and Cash Equivalents, Amortized Cost	61,198,000	65,016,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	61,198,000	65,016,000
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,698,000	9,900,000
Gross Unrealized Gains	0
Gross Unrealized Losses	(3,000)
Amounts Included In Cash And Cash Equivalents [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	72,237,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	72,237,000	75,326,000
Short-term Investments [Member] | Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains		1,000
Gross Unrealized Losses		(4,000)
Fair Value	$ 9,695,000	$ 9,897,000
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Average remaining contractual maturity of marketable securities	1 year
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Average remaining contractual maturity of marketable securities	12 months	12 months