Investments (Amortized Cost and Estimated Fair Value of Investments in Debt and Equity Securities by Category) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Investments, Amortized Cost	$ 610,591	$ 639,015
Investments, Gross Unrealized Gains	28,294	25,734
Investments, Gross Unrealized Losses	(9,085)	(3,416)
Investments, Fair Value	629,800	661,333
Other Investments [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	3,763	3,763
Investments, Gross Unrealized Gains		61
Investments, Gross Unrealized Losses	(703)
Investments, Fair Value	3,060	3,824
Equity Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	40,308	30,253
Investments, Gross Unrealized Gains	21,446	23,014
Investments, Gross Unrealized Losses	(3,840)	(1,504)
Investments, Fair Value	57,914	51,763
Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	566,520	604,999
Investments, Gross Unrealized Gains	6,848	2,659
Investments, Gross Unrealized Losses	(4,542)	(1,912)
Investments, Fair Value	568,826	605,746
Us Treasury Securities and Obligations of U.S. Government [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	47,852	50,088
Investments, Gross Unrealized Gains		7
Investments, Gross Unrealized Losses	(719)	(148)
Investments, Fair Value	47,133	49,947
Corporate Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	250,817	278,611
Investments, Gross Unrealized Gains	366	1,204
Investments, Gross Unrealized Losses	(1,899)	(742)
Investments, Fair Value	249,284	279,073
Collateralized Corporate Bank Loans [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	130,377	125,536
Investments, Gross Unrealized Gains	337	702
Investments, Gross Unrealized Losses	(470)	(301)
Investments, Fair Value	130,244	125,937
Municipal Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	124,396	134,052
Investments, Gross Unrealized Gains	6,127	709
Investments, Gross Unrealized Losses	(926)	(505)
Investments, Fair Value	129,597	134,256
Mortgage Backed [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	13,078	16,712
Investments, Gross Unrealized Gains	18	37
Investments, Gross Unrealized Losses	(528)	(216)
Investments, Fair Value	$ 12,568	$ 16,533

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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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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Sum of the carrying amounts as of the balance sheet date of all investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(h))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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