Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2011

Fair Value Measurements [Abstract]

Schedule of assets and liabilities measured at fair value on a recurring basis

	Quoted Market Prices (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
As of September 30, 2011:
Short-term investments:
Short-term municipal bond fund	$	20,520	$	—	$	—	$	20,520
Commercial paper		13,971		—		—		13,971
Corporate notes and bonds		42,096		—		—		42,096
Marketable securities:
Corporate notes and bonds		76,325		—		—		76,325
U.S. government agencies		13,154		—		—		13,154
Total	$	166,066	$	—	$	—	$	166,066
As of December 31, 2010:
Short-term investments:
Short-term municipal bond fund	$	20,275	$	—	$	—	$	20,275
Total	$	20,275	$	—	$	—	$	20,275

Schedule of carrying amounts and fair values of financial instruments

	September 30, 2011				December 31, 2010
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Cash and cash equivalents	$	189,741	$	189,741	$	376,951	$	376,951
Long-term debt	$	184,695	$	232,300	$	178,107	$	239,533