Fair Value Measurements (Detail Textuals) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, which primarily include money market funds	$ 75,755	$ 71,074	$ 101,058	$ 46,577
Corporate debt securities | Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value on recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities, fair value	2,020	2,010
Money market funds (included in cash and cash equivalents) | Fair Value Measurement, Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value on recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents, which primarily include money market funds	$ 67,084	$ 67,050