Investment in Securities, Summary of Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	$ 21,418,000	$ 0	$ 21,418,000	$ 17,540,000
Gross unrealized gains	20,011,000		20,011,000	19,205,000
Gross unrealized losses	0		0	0
Fair value	41,429,000	0	41,429,000	36,745,000
Changes in net unrealized gain (loss), net of tax	2,321,000		1,019,000
Proceeds from sale of investment available for sale	321,000	0	321,000
Gross realized gains on sale of investment available for sale	20,000		20,000
Gross realized losses on sale of investment available for sale	0		0
Common Stock [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	21,319,000	0	21,319,000	17,441,000
Gross unrealized gains	19,996,000		19,996,000	19,196,000
Gross unrealized losses	0		0	0
Fair value	41,315,000	0	41,315,000	36,637,000
Closed-end Funds [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	99,000	0	99,000	99,000
Gross unrealized gains	15,000		15,000	9,000
Gross unrealized losses	0		0	0
Fair value	$ 114,000	$ 0	$ 114,000	$ 108,000