Fair Value Measurement - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands	Sep. 30, 2011		Dec. 31, 2010		Sep. 30, 2010
Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	$ 149,966	[1]	$ 226,009	[1]	$ 210,189	[1]
Equity securities - mutual funds			14,411	[1]	5,380	[1]
Total	149,966	[1]	240,420	[1]	215,569	[1]
Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	0	[2]	0	[2]	0	[2]
Equity securities - mutual funds			0	[2]	0	[2]
Total	0	[2]	0	[2]	0	[2]
Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	0	[3]	0	[3]	0	[3]
Equity securities - mutual funds			0	[3]	0	[3]
Total	0	[3]	0	[3]	0	[3]
Estimate of Fair Value, Fair Value Disclosure [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	149,966		226,009		210,189
Equity securities - mutual funds			14,411		5,380
Total	$ 149,966		$ 240,420		$ 215,569

[1] Quoted prices in active markets for identical assets or liabilities.

[2] Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

[3] Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.