Investments - Classification (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Investment [Line Items]
Total investments, fair value	$ 70,162		$ 83,296
Equity securities - mutual funds [Member]
Investment [Line Items]
Marketable securities	2,810		2,869
Total fixed maturity securities [Member]
Investment [Line Items]
Marketable securities	66,744		79,819
US Government-backed securities [Member]
Investment [Line Items]
Marketable securities	0		68,497
Agency bonds [Member]
Investment [Line Items]
Marketable securities	58,533		5,000
Commercial paper [Member]
Investment [Line Items]
Marketable securities	5,000		0
Certificates of deposit [Member]
Investment [Line Items]
Marketable securities	3,211		6,322
Cost-method investments [Member]
Investment [Line Items]
Cost method investments	608	[1]	608	[1]
Short-term investments [Member]
Investment [Line Items]
Total investments, fair value	16,213		44,026
Short-term investments [Member] | Equity securities - mutual funds [Member]
Investment [Line Items]
Marketable securities	0		0
Short-term investments [Member] | Total fixed maturity securities [Member]
Investment [Line Items]
Marketable securities	16,213		44,026
Short-term investments [Member] | US Government-backed securities [Member]
Investment [Line Items]
Marketable securities	0		35,989
Short-term investments [Member] | Agency bonds [Member]
Investment [Line Items]
Marketable securities	8,002		5,000
Short-term investments [Member] | Commercial paper [Member]
Investment [Line Items]
Marketable securities	5,000		0
Short-term investments [Member] | Certificates of deposit [Member]
Investment [Line Items]
Marketable securities	3,211		3,037
Short-term investments [Member] | Cost-method investments [Member]
Investment [Line Items]
Cost method investments	0		0
Long-term investments [Member]
Investment [Line Items]
Total investments, fair value	53,341		38,662
Long-term investments [Member] | Equity securities - mutual funds [Member]
Investment [Line Items]
Marketable securities	2,810		2,869
Long-term investments [Member] | Total fixed maturity securities [Member]
Investment [Line Items]
Marketable securities	50,531		35,793
Long-term investments [Member] | US Government-backed securities [Member]
Investment [Line Items]
Marketable securities	0		32,508
Long-term investments [Member] | Agency bonds [Member]
Investment [Line Items]
Marketable securities	50,531		0
Long-term investments [Member] | Commercial paper [Member]
Investment [Line Items]
Marketable securities	0		0
Long-term investments [Member] | Certificates of deposit [Member]
Investment [Line Items]
Marketable securities	0		3,285
Long-term investments [Member] | Cost-method investments [Member]
Investment [Line Items]
Cost method investments	0		0
Other assets [Member]
Investment [Line Items]
Total investments, fair value	608		608
Other assets [Member] | Equity securities - mutual funds [Member]
Investment [Line Items]
Marketable securities	0		0
Other assets [Member] | Total fixed maturity securities [Member]
Investment [Line Items]
Marketable securities	0		0
Other assets [Member] | US Government-backed securities [Member]
Investment [Line Items]
Marketable securities	0		0
Other assets [Member] | Agency bonds [Member]
Investment [Line Items]
Marketable securities	0		0
Other assets [Member] | Commercial paper [Member]
Investment [Line Items]
Marketable securities	0		0
Other assets [Member] | Certificates of deposit [Member]
Investment [Line Items]
Marketable securities	0		0
Other assets [Member] | Cost-method investments [Member]
Investment [Line Items]
Cost method investments	$ 608		$ 608

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