Investments - Amortized Costs and Estimated Fair Values (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Schedule of Investments [Line Items]
Total investments, amortized cost	$ 70,133		$ 83,177
Total investments, gross unrealized gains	31		121
Total investments, gross unrealized losses	(2)		(2)
Total investments, fair value	70,162		83,296
Realized investment gains (losses)	0		0		0
Equity securities - mutual funds [Member]
Schedule of Investments [Line Items]
Trading securities, amortized cost	2,810		2,750
Trading securities, gross unrealized gains	0		119
Trading securities, gross unrealized losses	0		0
Trading securities, fair value	2,810		2,869
Total available for sale marketable securities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, amortized cost basis	66,715		79,819
Available-for-sale securities, gross unrealized gains	31		2
Available-for-sale securities, gross unrealized losses	(2)		(2)
Available-for-sale securities, fair value	66,744		79,819
US Government-backed securities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, amortized cost basis			68,495
Available-for-sale securities, gross unrealized gains			2
Available-for-sale securities, gross unrealized losses			0
Available-for-sale securities, fair value			68,497
Agency bonds [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, amortized cost basis	58,508	[1]	5,000	[1]
Available-for-sale securities, gross unrealized gains	27	[1]	0	[1]
Available-for-sale securities, gross unrealized losses	(2)	[1]	0	[1]
Available-for-sale securities, fair value	58,533	[1]	5,000	[1]
Commercial paper [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, amortized cost basis	5,000
Available-for-sale securities, gross unrealized gains	0
Available-for-sale securities, gross unrealized losses	0
Available-for-sale securities, fair value	5,000
Certificates of deposit [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, amortized cost basis	3,207		6,324
Available-for-sale securities, gross unrealized gains	4		0
Available-for-sale securities, gross unrealized losses	0		(2)
Available-for-sale securities, fair value	3,211		6,322
Cost-method investments [Member]
Schedule of Investments [Line Items]
Cost method investments	608	[2]	608	[2]
Cost method investments, gross unrealized gains	0	[2]	0	[2]
Cost method investments, gross unrealized losses	0	[2]	0	[2]
Cost method investments, fair value	$ 608	[2]	$ 608	[2]

[1] Agency bonds are securities backed by U.S. government-sponsored entities.

[2] Investments for which it is not practical to estimate fair value are included at cost and primarily consist of investments in privately-held companies.