Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets:
Marketable securities	$ 39,026us-gaap_MarketableSecuritiesCurrent	$ 37,940us-gaap_MarketableSecuritiesCurrent
Long term marketable securities	27,315us-gaap_MarketableSecuritiesNoncurrent	19,816us-gaap_MarketableSecuritiesNoncurrent
Liabilities:
Derivative liabilities	2,691us-gaap_DerivativeLiabilitiesNoncurrent	6,564us-gaap_DerivativeLiabilitiesNoncurrent
Quoted Prices in Active Markets (Level 1)
Assets:
Cash and cash equivalents	25,810	36,396
Total assets at fair value	25,810	36,396
Significant Other Observable Inputs (Level 2)
Assets:
Marketable securities	39,026	37,940
Long term marketable securities	27,315	19,816
Marketable securities - restricted (SERP)	267	305
Total assets at fair value	66,608	58,061
Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative liabilities	2,691	6,564
Total Carrying Value
Assets:
Cash and cash equivalents	25,810	36,396
Marketable securities	39,026	37,940
Long term marketable securities	27,315	19,816
Marketable securities - restricted (SERP)	267	305
Total assets at fair value	92,418	94,457
Liabilities:
Derivative liabilities	$ 2,691	$ 6,564

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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For a classified balance sheet, the amount recognized in balance sheet as a current asset associated with the plan.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

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Total debt and equity financial instruments including: (1) securities held-to-maturity and (2) securities available-for-sale that will be held for the long-term.

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