Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets:
Marketable securities	$ 34,783	$ 49,211
Long term marketable securities	15,763	8,756
Liabilities:
Derivative liabilities	7,258	12,644
Quoted Prices in Active Markets (Level 1)
Assets:
Cash and cash equivalents	37,780	32,980
Total assets at fair value	37,780	32,980
Significant Other Observable Inputs (Level 2)
Assets:
Marketable securities	34,783	49,211
Long term marketable securities	15,763	8,756
Marketable securities - restricted (SERP)	305	305
Total assets at fair value	50,851	58,272
Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative liabilities	7,258	12,644
Total Carrying Value
Assets:
Cash and cash equivalents	37,780	32,980
Marketable securities	34,783	49,211
Long term marketable securities	15,763	8,756
Marketable securities - restricted (SERP)	305	305
Total assets at fair value	88,631	91,252
Liabilities:
Derivative liabilities	$ 7,258	$ 12,644