Investments in Marketable Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 75,857,000	$ 114,809,000
Net unrealized holding gains	0	1,000
Net unrealized holding losses	(3,000)	(1,000)
Fair Value	75,854,000	114,809,000
Maximum Term Of Available For Sale Securities	1 year	1 year
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	0	0	0
Available-for-sale - included in cash equivalents: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost		24,010,000
Net unrealized holding gains		0
Net unrealized holding losses		0
Fair Value		24,010,000
Available-for-sale - included in cash equivalents: | Money market funds and other
Schedule of Available-for-sale Securities [Line Items]
Cost	53,549,000	40,793,000
Net unrealized holding gains	0	0
Net unrealized holding losses	0	0
Fair Value	53,549,000	40,793,000
Available-for-sale - included in cash equivalents: | U.S. government-sponsored enterprise securities
Schedule of Available-for-sale Securities [Line Items]
Cost		4,000,000
Net unrealized holding gains		0
Net unrealized holding losses		0
Fair Value		4,000,000
Available-for-sale - included in short-term marketable securities: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost	14,933,000	12,704,000
Net unrealized holding gains	0	1,000
Net unrealized holding losses	(3,000)	0
Fair Value	14,930,000	12,705,000
Available-for-sale - included in short-term marketable securities: | Municipal notes
Schedule of Available-for-sale Securities [Line Items]
Cost		9,295,000
Net unrealized holding gains		0
Net unrealized holding losses		0
Fair Value		9,295,000
Available-for-sale - included in short-term marketable securities: | U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Cost	4,510,000	7,501,000
Net unrealized holding gains	0	0
Net unrealized holding losses	0	0
Fair Value	4,510,000	7,501,000
Available-for-sale - included in short-term marketable securities: | U.S. government-sponsored enterprise securities
Schedule of Available-for-sale Securities [Line Items]
Cost	1,065,000	16,506,000
Net unrealized holding gains	0	0
Net unrealized holding losses	0	(1,000)
Fair Value	1,065,000	16,505,000
Available-for-sale - included in short-term marketable securities: | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Cost	1,800,000
Net unrealized holding gains	0
Net unrealized holding losses	0
Fair Value	$ 1,800,000