Significant Accounting Policies Fair Value Measurements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			$ 140,034,000
Short-term interest rate reset dates of auction rate note securities	less than ninety days
Auction rate note securities with contractual maturities	excess of ten years
Reset period for the securities held	seven or twenty eight days
Comprehensive income (loss) net of tax due to auction rate notes	355,000		325,000		547,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	94,353,000
Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	32,891,000		78,983,000
Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	57,303,000		54,194,000
Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	4,159,000		6,857,000
Fair value of auction rate notes	4,700,000
Changes in Level 3 Securities [Roll Forward]
Beginning balance, December 31, 2011	6,857,000
Transfers in and/or out of Level 3
Total gains, before tax	402,000
Settlements	(3,100,000)
Ending balance, December 31, 2012	4,159,000
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			55,912,000	[1]
Money Market Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	13,845,000	[1]
Money Market Funds [Member] | Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	13,845,000	[1]	55,912,000	[1]
Money Market Funds [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[1]		[1]
Money Market Funds [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[1]		[1]
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			23,071,000	[2]
Certificates of Deposit [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	19,046,000	[2]
Certificates of Deposit [Member] | Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	19,046,000	[2]	23,071,000	[2]
Certificates of Deposit [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Certificates of Deposit [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			11,298,000	[2]
Municipal Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	12,404,000	[2]
Municipal Securities [Member] | Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Municipal Securities [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	12,404,000	[2]	11,298,000	[2]
Municipal Securities [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			33,396,000	[2]
Corporate Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	26,437,000	[2]
Corporate Debt Securities [Member] | Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Corporate Debt Securities [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	26,437,000	[2]	33,396,000	[2]
Corporate Debt Securities [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			4,989,000	[2]
Commercial Paper [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	18,462,000	[2]
Commercial Paper [Member] | Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Commercial Paper [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	18,462,000	[2]	4,989,000	[2]
Commercial Paper [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
U.S. Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			4,511,000	[2]
U.S. Agencies [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]
U.S. Agencies [Member] | Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
U.S. Agencies [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]	4,511,000	[2]
U.S. Agencies [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[2]		[2]
Auction rate notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis			6,857,000	[3]
Comprehensive income (loss) net of tax due to auction rate notes	(346,000)
Comprehensive income (loss) before tax due to auction rate notes	(543,000)
Auction rate notes [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	4,159,000	[3]
Auction rate notes [Member] | Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[3]		[3]
Auction rate notes [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis		[3]		[3]
Auction rate notes [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities measured at fair value on a recurring basis	$ 4,159,000	[3]	$ 6,857,000	[3]
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period for principal repayments by issuer	19 years
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period for principal repayments by issuer	35 years
Maximum [Member] | Auction rate notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate, percent in excess of one month LIBOR	1.50%		2.50%

[1] Included in cash and cash equivalents

[2] Included in short-term investments

[3] Included in long-term investments