Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets:
Marketable securities	$ 36,681	$ 37,940
Long term marketable securities	33,488	19,816
Liabilities:
Derivative liabilities	2,070	6,564
Total Carrying Value
Assets:
Cash and cash equivalents	33,110	36,396
Marketable securities	36,681	37,940
Long term marketable securities	33,488	19,816
Marketable securities - restricted (SERP)	267	305
Total assets at fair value	103,546	94,457
Liabilities:
Derivative liabilities	2,070	6,564
Quoted Prices in Active Markets (Level 1)
Assets:
Cash and cash equivalents	33,110	36,396
Total assets at fair value	33,110	36,396
Significant Other Observable Inputs (Level 2)
Assets:
Marketable securities	36,681	37,940
Long term marketable securities	33,488	19,816
Marketable securities - restricted (SERP)	267	305
Total assets at fair value	70,436	58,061
Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative liabilities	$ 2,070	$ 6,564