Fair Value of Financial Instruments (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	$ 98,677,000	$ 98,677,000	$ 109,086,000
Summary of change in balance sheet carrying values associated with Level 3 financial instruments [Roll Forward]
Balance at December 31, 2011		998,000
Purchases		0
Settlements (at par)		0
Transfers in/out of Level 3		0
Gains
Realized		0
Unrealized		0
Losses [Abstract]
Realized		0
Unrealized		(35,000)
Balance at June 30, 2012	963,000	963,000
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	97,714,000	97,714,000	108,088,000
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	963,000	963,000	998,000
Cash and cash equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	56,050,000	56,050,000	63,077,000
Cash and cash equivalents [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	56,050,000	56,050,000	63,077,000
Cash and cash equivalents [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Cash and cash equivalents [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	30,143,000	30,143,000	24,740,000
Held-to-maturity securities	30,100,000	30,100,000
Short-term investments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	30,143,000	30,143,000	24,740,000
Short-term investments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Short-term investments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	11,521,000	11,521,000	20,271,000
Held-to-maturity securities	11,500,000	11,500,000	20,300,000
Other Investments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	11,521,000	11,521,000	20,271,000
Other Investments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Other Investments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Auction Rate Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	963,000	963,000	998,000
Investment par value	1,300,000	1,300,000	1,300,000
Held-to-maturity Securities, Debt Maturities, Date	Dec. 01, 2045
Summary of change in balance sheet carrying values associated with Level 3 financial instruments [Roll Forward]
Balance at December 31, 2011		998,000
Purchases		0
Settlements (at par)		0
Transfers in/out of Level 3		0
Gains
Realized		0
Unrealized		0
Losses [Abstract]
Realized		0
Unrealized		(35,000)
Balance at June 30, 2012	963,000	963,000
Held-to-maturity securities in a continuous unrealized loss position for more than 12 months	963,000	963,000
Auction rate securities, fair value	1,000,000	1,000,000
Auction Rate Municipal Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Auction Rate Municipal Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	0	0	0
Auction Rate Municipal Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a recurring basis	963,000	963,000	998,000
US Agency Bonds [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term			13 days
US Agency Bonds [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term			8 months 12 days
US Agency Bonds [Member] | Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity securities	7,000,000	7,000,000	4,000,000
US Agency Bonds [Member] | Short-term investments [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	2 months 12 days	2 months 12 days
US Agency Bonds [Member] | Short-term investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	1 year	1 year
US Agency Bonds [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity securities	5,000,000	5,000,000	8,100,000
US Agency Bonds [Member] | Other Investments [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	1 year 1 month 6 days	1 year 1 month 6 days	1 year 2 months 12 days
US Agency Bonds [Member] | Other Investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	1 year 10 months 24 days	1 year 10 months 24 days	1 year 10 months 24 days
Commercial Paper [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term			9 days
Commercial Paper [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term			7 months 6 days
Commercial Paper [Member] | Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity securities	14,000,000	14,000,000	18,700,000
Commercial Paper [Member] | Short-term investments [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	1 month 6 days	1 month 6 days
Commercial Paper [Member] | Short-term investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	4 months 24 days	4 months 24 days
Commercial Paper [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity securities			10,200,000
Commercial Paper [Member] | Other Investments [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term			1 year 1 month 6 days
Commercial Paper [Member] | Other Investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term			1 year 7 months 6 days
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term			7 months 6 days
Corporate Bonds [Member] | Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity securities	9,100,000	9,100,000	2,000,000
Corporate Bonds [Member] | Short-term investments [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	1 month 6 days	1 month 6 days
Corporate Bonds [Member] | Short-term investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	9 months 18 days	9 months 18 days
Corporate Bonds [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity securities	3,000,000	3,000,000
Maturity term	1 year 1 month 6 days	1 year 1 month 6 days
US Treasuries [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity securities	$ 3,500,000	$ 3,500,000	$ 2,000,000
Maturity term			1 year 7 months 6 days
US Treasuries [Member] | Other Investments [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	1 year 1 month 6 days	1 year 1 month 6 days
US Treasuries [Member] | Other Investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity term	1 year 9 months 18 days	1 year 9 months 18 days