Investments - Tables (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Debt securities: corporate bonds, Cost	$ 4,306,000	$ 4,458,000
Cost	14,706,000	14,797,000
Gross Unrealized Gains	10,409,000	7,925,000
Gross Unrealized Losses	(44,000)	(132,000)
Debt securities: corporate bonds, Carrying Value	4,382,000	4,453,000
Carrying Value	25,071,000	22,590,000
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost, Due in one year or less	182,000	38,000
Amortized Cost, Due after one year through five years	4,124,000	2,603,000
Amortized Cost, Due after five years		1,817,000
Amortized Cost	4,306,000	4,458,000
Carrying Value, Due in one year or less	183,000	37,000
Carrying Value, Due after one year through five years	4,199,000	2,566,000
Carrying Value, Due after five years		1,850,000
Carrying Value	4,382,000	4,453,000
Gross realized gains:	610,000	1,429,000	$ 5,552,000
Gross realized losses:	(4,615,000)	(21,024,000)	(1,897,000)
Net realized gain (loss)	(4,005,000)	(19,595,000)	3,655,000
Investment in unconsolidated affiliate, loss	2,170,000	20,696,000
Impairment loss on investment in unconsolidated affiliate	2,170,000	20,696,000	1,078,000
Other Investments	1,312,000	3,482,000
Synthonics
Available-for-sale Securities, Debt Maturities [Abstract]
Cost method investments	$ 0	$ 2,170,000
Cost Method, Ownership Percentage	18.20%	18.30%
Mindjet
Available-for-sale Securities, Debt Maturities [Abstract]
Impairment loss on investment in unconsolidated affiliate		$ 20,700,000	1,100,000
Other Investments	$ 2,300,000	$ 2,300,000
Voting Interest Percentage		19.30%
Corporate Bond Securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities: corporate bonds, Cost	4,306,000	$ 4,458,000
Gross Unrealized Gains	82,000	46,000
Gross Unrealized Losses	(6,000)	(51,000)
Debt securities: corporate bonds, Carrying Value	4,382,000	4,453,000
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost	4,306,000	4,458,000
Carrying Value	4,382,000	4,453,000
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities, Cost	10,400,000	10,339,000
Gross Unrealized Gains	10,327,000	7,879,000
Gross Unrealized Losses	(38,000)	(81,000)
Marketable equity securities, Carrying Value	20,689,000	18,137,000
Equity Securities | Mindjet
Available-for-sale Securities, Debt Maturities [Abstract]
Cost method investments	$ 1,312,000	$ 1,312,000
Cost Method, Ownership Percentage
Equity Method Investments	$ 0	$ 0
Equity Method Investment, Ownership Percentage	19.30%	19.30%
Other Investments	$ 1,312,000	$ 1,312,000
Voting Interest Percentage	19.30%	19.30%
Debt Securities
Available-for-sale Securities, Debt Maturities [Abstract]
Gross realized gains:		$ 419,000	7,000
Gross realized losses:	(90,000)	(4,000)	(116,000)
Equity Securities and Other Investments
Available-for-sale Securities, Debt Maturities [Abstract]
Gross realized gains:	610,000	1,010,000	5,545,000
Gross realized losses:	$ (4,525,000)	$ (21,020,000)	$ (1,781,000)