Summary of Significant Accounting Policies (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2012
Amortized Cost
Amortized Cost	74,718
Unrealized Gains
Unrealized Gains	1
Unrealized Losses
Unrealized Losses	(50)
Fair Value
Fair Value	74,669
Number of securities in unrealized loss position for less than 12 months	22
Aggregate fair value of marketable securities in unrealized loss position
Aggregate Fair Value	66,171
Unrealized loss position
Unrealized Losses	(50)
Corporate debt securities
Amortized Cost
Amortized Cost	73,718
Unrealized Gains
Unrealized Gains	1
Unrealized Losses
Unrealized Losses	(49)
Fair Value
Fair Value	73,670
Aggregate fair value of marketable securities in unrealized loss position
Aggregate Fair Value	65,172
Unrealized loss position
Unrealized Losses	(49)
U.S. Government agencies securities
Amortized Cost
Amortized Cost	1,000
Unrealized Losses
Unrealized Losses	(1)
Fair Value
Fair Value	999
Aggregate fair value of marketable securities in unrealized loss position
Aggregate Fair Value	999
Unrealized loss position
Unrealized Losses	(1)
Minimum
Available-for-sale securities
Expected average maturities period of marketable securities classified as available-for-sale	3 months
Maximum
Available-for-sale securities
Expected average maturities period of marketable securities classified as available-for-sale	12 months

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Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for securities categorized neither as held-to-maturity nor trading securities.

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