Investment in Securities, Investment in Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Available for sale securities [Abstract]
Cost		$ 122,636	$ 200,051
Fair value		135,952	221,535
Total investments in securities [Abstract]
Cost	$ 360,197	331,585	308,089
Fair value	360,448	352,637	323,110
Common Stocks [Member]
Available for sale securities [Abstract]
Cost		65,331	130,869
Fair value		65,024	129,990
Mutual Funds [Member]
Available for sale securities [Abstract]
Cost		3,523	4,593
Fair value		4,710	6,422
Investment in Securities [Member] \| Debt and Equity Securities [Member]
Debt and equity securities [Abstract]
Cost	360,197	266,151	177,014
Fair value	360,448	287,342	192,609
Investment in Securities [Member] \| Debt and Equity Securities [Member] \| Government Obligations [Member]
Debt and equity securities [Abstract]
Cost	86,039	53,681	99,687
Fair value	86,242	53,804	99,820
Investment in Securities [Member] \| Debt and Equity Securities [Member] \| Common Stocks [Member]
Debt and equity securities [Abstract]
Cost	271,415	209,686	71,511
Fair value	267,708	228,557	85,802
Investment in Securities [Member] \| Debt and Equity Securities [Member] \| Mutual Funds [Member]
Debt and equity securities [Abstract]
Cost	2,063	1,959	2,405
Fair value	3,393	3,157	3,333
Investment in Securities [Member] \| Debt and Equity Securities [Member] \| Other Investments [Member]
Debt and equity securities [Abstract]
Cost	680	825	3,411
Fair value	3,105	1,824	3,654
Investment in Securities [Member] \| Available for Sale Securities [Member]
Available for sale securities [Abstract]
Cost	0	65,434	131,075
Fair value	0	65,295	130,501
Investment in Securities [Member] \| Available for Sale Securities [Member] \| Common Stocks [Member]
Available for sale securities [Abstract]
Cost	0	65,331	130,869
Fair value	0	65,024	129,990
Investment in Securities [Member] \| Available for Sale Securities [Member] \| Mutual Funds [Member]
Available for sale securities [Abstract]
Cost	0	103	206
Fair value	$ 0	$ 271	$ 511

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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Cost of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

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