Investment in Securities, Summary of Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	$ 18,872,000	$ 18,872,000	$ 0	$ 17,540,000
Gross unrealized gains	16,326,000	16,326,000		19,205,000
Gross unrealized losses	0	0		0
Fair value	35,198,000	35,198,000	0	36,745,000
Changes in net unrealized gain (loss), net of tax	1,259,000	(1,302,000)
Proceeds from sale of investment available for sale	0	0
Gross realized gains on sale of investment available for sale	0	0
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	18,773,000	18,773,000	0	17,441,000
Gross unrealized gains	16,315,000	16,315,000		19,196,000
Gross unrealized losses	0	0		0
Fair value	35,088,000	35,088,000	0	36,637,000
Closed-end Funds [Member]
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Cost	99,000	99,000	0	99,000
Gross unrealized gains	11,000	11,000		9,000
Gross unrealized losses	0	0		0
Fair value	$ 110,000	$ 110,000	$ 0	$ 108,000

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

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- References

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- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

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- Definition

Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities and unrealized holding gain (loss) related to transfers of securities into the available-for-sale classification and out of the held-to-maturity classification.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

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- Definition

Amount of cash inflow from sale, maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3151-108585

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 12
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

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