Significant Accounting Policies, Fair Value Disclosures (Details) (Recurring [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Changes in fair value of our Level 3 financial asset [Roll Forward]
Money market funds	$ 14,437	$ 17,235
Certificates of deposits	1,160	1,879
Commercial paper	3,247	5,745
Corporate notes and bonds	25,756	20,173
Municipal securities	201
U.S. government agency securities	1,509	202
Total	46,310	45,234
Level 1 [Member]
Changes in fair value of our Level 3 financial asset [Roll Forward]
Money market funds	14,437	17,235
Certificates of deposits	1,160	1,879
Commercial paper	0	0
Corporate notes and bonds	0	0
Municipal securities	0
U.S. government agency securities	0	0
Total	15,597	19,114
Level 2 [Member]
Changes in fair value of our Level 3 financial asset [Roll Forward]
Money market funds	0	0
Certificates of deposits	0	0
Commercial paper	3,247	5,745
Corporate notes and bonds	25,756	20,173
Municipal securities	201
U.S. government agency securities	1,509	202
Total	30,713	26,120
Level 3 [Member]
Changes in fair value of our Level 3 financial asset [Roll Forward]
Money market funds	0	0
Certificates of deposits	0	0
Commercial paper	0	0
Corporate notes and bonds	0	0
Municipal securities	0
U.S. government agency securities	0	0
Total	$ 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 includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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