| Financial Instruments (Details 1) (USD $) In Thousands, unless otherwise specified | Jun. 30, 2012 | Dec. 31, 2011 | 
|---|---|---|
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | $ 72,161 | $ 72,082 | 
| Money market funds [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 378 | 14,372 | 
| Fair Value Measurements Recurring [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 72,161 | 72,082 | 
| Fair Value Measurements Recurring [Member] | Government debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 12,000 | 15,969 | 
| Fair Value Measurements Recurring [Member] | Corporate debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 59,783 | 41,741 | 
| Fair Value Measurements Recurring [Member] | Money market funds [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 378 | 14,372 | 
| Fair Value Measurements Recurring [Member] | Quoted prices In Active Market For Identical Assets (Level 1) [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 378 | 14,372 | 
| Fair Value Measurements Recurring [Member] | Quoted prices In Active Market For Identical Assets (Level 1) [Member] | Government debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | ||
| Fair Value Measurements Recurring [Member] | Quoted prices In Active Market For Identical Assets (Level 1) [Member] | Corporate debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | ||
| Fair Value Measurements Recurring [Member] | Quoted prices In Active Market For Identical Assets (Level 1) [Member] | Money market funds [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 378 | 14,372 | 
| Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 71,783 | 57,710 | 
| Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Government debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 12,000 | 15,969 | 
| Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | 59,783 | 41,741 | 
| Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money market funds [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | ||
| Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | ||
| Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Government debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | ||
| Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate debt securities [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities | ||
| Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money market funds [Member] | ||
| Financial instruments measured on recurring basis | ||
| Fair value, available-for-sale securities |