Fair Value Measurements Fair Value Heirarchy (Details) (USD $)
In Thousands, unless otherwise specified |
3 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Mar. 31, 2013
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Mar. 31, 2013
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
Fair value [Member]
|
Dec. 31, 2012
Fair value [Member]
|
Mar. 31, 2013
Corporate Bonds
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
Corporate Bonds
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
Corporate Bonds
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
Corporate Bonds
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
Corporate Bonds
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
Corporate Bonds
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
Corporate Bonds
Fair value [Member]
|
Dec. 31, 2012
Corporate Bonds
Fair value [Member]
|
Mar. 31, 2013
Commercial Paper
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
Commercial Paper
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
Commercial Paper
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
Commercial Paper
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
Commercial Paper
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
Commercial Paper
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
Commercial Paper
Fair value [Member]
|
Dec. 31, 2012
Commercial Paper
Fair value [Member]
|
Mar. 31, 2013
Negotiable Certificates of Deposit
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
Negotiable Certificates of Deposit
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
Negotiable Certificates of Deposit
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
Negotiable Certificates of Deposit
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
Negotiable Certificates of Deposit
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
Negotiable Certificates of Deposit
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
Negotiable Certificates of Deposit
Fair value [Member]
|
Dec. 31, 2012
Negotiable Certificates of Deposit
Fair value [Member]
|
Mar. 31, 2013
US Treasury Notes
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
US Treasury Notes
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
US Treasury Notes
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
US Treasury Notes
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
US Treasury Notes
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
US Treasury Notes
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
US Treasury Notes
Fair value [Member]
|
Dec. 31, 2012
US Treasury Notes
Fair value [Member]
|
Mar. 31, 2013
Agencies Securities
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
Agencies Securities
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
Agencies Securities
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
Agencies Securities
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
Agencies Securities
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
Agencies Securities
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
Agencies Securities
Fair value [Member]
|
Dec. 31, 2012
Agencies Securities
Fair value [Member]
|
Mar. 31, 2013
Municipal Bonds
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
Municipal Bonds
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
Municipal Bonds
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
Municipal Bonds
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
Municipal Bonds
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
Municipal Bonds
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
Municipal Bonds
Fair value [Member]
|
Dec. 31, 2012
Municipal Bonds
Fair value [Member]
|
Mar. 31, 2013
Asset-backed Securities
Fair Value, Inputs, Level 1 [Member]
|
Dec. 31, 2012
Asset-backed Securities
Fair Value, Inputs, Level 1 [Member]
|
Mar. 31, 2013
Asset-backed Securities
Fair Value, Inputs, Level 2 [Member]
|
Dec. 31, 2012
Asset-backed Securities
Fair Value, Inputs, Level 2 [Member]
|
Mar. 31, 2013
Asset-backed Securities
Fair Value, Inputs, Level 3 [Member]
|
Dec. 31, 2012
Asset-backed Securities
Fair Value, Inputs, Level 3 [Member]
|
Mar. 31, 2013
Asset-backed Securities
Fair value [Member]
|
Dec. 31, 2012
Asset-backed Securities
Fair value [Member]
|
|
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Fair Value, Equity Level Transfer | 0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Available-for-sale Securities, Fair Value Disclosure | $ 0 | $ 0 | $ 163,185 | $ 183,787 | $ 0 | $ 0 | $ 163,185 | $ 183,787 | $ 0 | $ 0 | $ 33,683 | $ 37,357 | $ 0 | $ 0 | $ 33,683 | $ 37,357 | $ 0 | $ 0 | $ 45,144 | $ 55,748 | $ 0 | $ 0 | $ 45,144 | $ 55,748 | $ 0 | $ 0 | $ 4,411 | $ 4,414 | $ 0 | $ 0 | $ 4,411 | $ 4,414 | $ 0 | $ 0 | $ 17,494 | $ 22,267 | $ 0 | $ 0 | $ 17,494 | $ 22,267 | $ 0 | $ 0 | $ 25,545 | $ 25,867 | $ 0 | $ 0 | $ 25,545 | $ 25,867 | $ 0 | $ 0 | $ 12,747 | $ 11,568 | $ 0 | $ 0 | $ 12,747 | $ 11,568 | $ 0 | $ 0 | $ 24,161 | $ 26,566 | $ 0 | $ 0 | $ 24,161 | $ 26,566 |