Cash and Cash Equivalents, Short-term Investments and Fair Value of Financial Instruments avail for sale securities levels 1-2-3 table (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, and Short-term Investments	$ 104,531	$ 62,313
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	65,708	38,891
Fair Value, Measurements, Recurring [Member]
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, and Short-term Investments	65,708	38,891
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	65,708	38,891
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, and Short-term Investments	65,708	38,891
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	65,708	38,891
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, and Short-term Investments	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, and Short-term Investments	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		$ 0