Fair Value of Financial Instruments (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Assets:
Marketable securities	$ 32,061,000	$ 37,940,000	$ 34,783,000
Long term marketable securities	43,967,000	19,816,000	15,763,000
Liabilities:
Derivative liabilities	1,156,000	6,564,000	7,258,000
Recurring
Assets:
Cash and cash equivalents	25,641,000	36,396,000	37,780,000
Marketable securities	32,061,000	37,940,000	34,783,000
Long term marketable securities	43,967,000	19,816,000	15,763,000
Marketable securities - restricted (SERP)	267,000	305,000	305,000
Total assets at fair value	101,936,000	94,457,000	88,631,000
Liabilities:
Derivative liabilities	1,156,000	6,564,000	7,258,000
Quoted Prices in Active Markets (Level 1) | Recurring
Assets:
Cash and cash equivalents	25,641,000	36,396,000	37,780,000
Marketable securities	653,000
Marketable securities - restricted (SERP)	267,000
Total assets at fair value	26,561,000	36,396,000	37,780,000
Significant Other Observable Inputs (Level 2) | Recurring
Assets:
Marketable securities	31,408,000	37,940,000	34,783,000
Long term marketable securities	43,967,000	19,816,000	15,763,000
Marketable securities - restricted (SERP)		305,000	305,000
Total assets at fair value	75,375,000	58,061,000	50,851,000
Significant Unobservable Inputs (Level 3) | Recurring
Liabilities:
Derivative liabilities	1,156,000	$ 6,564,000	$ 7,258,000
Warrants outstanding	$ 0