Cash Equivalents and Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Y	Dec. 31, 2010
Cash Equivalents and Marketable Securities
Maturity period for long-term debt classified as available-for-sale (in years)	1
Summary of marketable securities
Amortized Cost	$ 70,838	$ 70,063
Gross Unrealized Gains	15	18
Gross Unrealized Losses Less than 12 Months	(28)	0
Aggregate Fair Value	72,360	85,075
Amortized Cost
Matures in less than one year	69,921
Matures in one to three years	917
Total	70,838
Aggregate Fair Value
Matures in less than one year	69,908
Matures in one to three years	917
Aggregate Fair Value	72,360	85,075
Fair Value
Less than 12 months	37,725
Total	37,725
Unrealized losses
Less than 12 months, gross	(28)	0
Total	(28)
Corporate debt securities
Summary of marketable securities
Amortized Cost	52,606	22,597
Gross Unrealized Gains	10	6
Gross Unrealized Losses Less than 12 Months	(11)	0
Aggregate Fair Value	52,605	22,600
Aggregate Fair Value
Aggregate Fair Value	52,605	22,600
Fair Value
Less than 12 months	30,811
Total	30,811
Unrealized losses
Less than 12 months, gross	(11)	0
Total	(11)
US government debt securities
Summary of marketable securities
Amortized Cost	11,318	47,466
Gross Unrealized Gains	5	12
Gross Unrealized Losses Less than 12 Months		(3)
Aggregate Fair Value	11,323	62,475
Aggregate Fair Value
Aggregate Fair Value	11,323	62,475
Unrealized losses
Less than 12 months, gross		(3)
Foreign government debt securities
Summary of marketable securities
Amortized Cost	6,914
Gross Unrealized Losses Less than 12 Months	(17)
Aggregate Fair Value	8,432
Aggregate Fair Value
Aggregate Fair Value	8,432
Fair Value
Less than 12 months	6,914
Total	6,914
Unrealized losses
Less than 12 months, gross	(17)
Total	$ (17)