Investment in Securities, Summary of Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	$ 18,838,000	$ 17,898,000
Gross unrealized gains	18,393,000	14,709,000
Gross unrealized losses	0	0
Fair value	37,231,000	32,607,000
Unrealized changes to fair value net of taxes included in other comprehensive income	2,300,000	(5,500,000)	$ (600,000)
Amount reclassified from other comprehensive income	800,000	2,800,000	4,600,000
Proceeds from sale of investment available for sale	408,000	81,000	3,877,000
Gross realized gains on sale of investments available for sale	4,000	6,000	600,000
Gross realized losses on sale of investments available for sale	0	0	$ 0
Common Stock [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	18,739,000	17,898,000
Gross unrealized gains	18,392,000	14,709,000
Gross unrealized losses	0	0
Fair value	37,131,000	$ 32,607,000
Closed-end Funds [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	99,000
Gross unrealized gains	1,000
Gross unrealized losses	0
Fair value	$ 100,000