Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Dec. 31, 2013
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value	$ 83,822	$ 83,073
Fair Value, Measurements, Recurring [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value	81,065	79,257
Cash equivalents [Abstract]
Money market funds	5,736	9,926
Commercial paper	2,250	2,500
Marketable investments [Abstract]
Available for sale securities	73,079	66,831
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value	5,736	9,926
Cash equivalents [Abstract]
Money market funds	5,736	9,926
Commercial paper	0	0
Marketable investments [Abstract]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value	75,329	69,331
Cash equivalents [Abstract]
Money market funds	0	0
Commercial paper	2,250	2,500
Marketable investments [Abstract]
Available for sale securities	73,079	66,831
Maximum maturity period of investments	36 months
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value	0	0
Cash equivalents [Abstract]
Money market funds	0	0
Commercial paper	0	0
Marketable investments [Abstract]
Available for sale securities	$ 0	$ 0

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details