Investments (Amortized Cost and Estimated Fair Value of Investments in Debt and Equity Securities by Category) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Investments, Amortized Cost	$ 635,006	$ 639,015
Investments, Gross Unrealized Gains	25,403	25,734
Investments, Gross Unrealized Losses	(8,287)	(3,416)
Investments, Fair Value	652,122	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	(302)
Investments, Fair Value	3,461	3,824
Equity Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	35,762	30,253
Investments, Gross Unrealized Gains	21,238	23,014
Investments, Gross Unrealized Losses	(4,185)	(1,504)
Investments, Fair Value	52,815	51,763
Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	595,481	604,999
Investments, Gross Unrealized Gains	4,165	2,659
Investments, Gross Unrealized Losses	(3,800)	(1,912)
Investments, Fair Value	595,846	605,746
Us Treasury Securities and Obligations of U.S. Government [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	49,972	50,088
Investments, Gross Unrealized Gains		7
Investments, Gross Unrealized Losses	(554)	(148)
Investments, Fair Value	49,418	49,947
Corporate Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	257,521	278,611
Investments, Gross Unrealized Gains	557	1,204
Investments, Gross Unrealized Losses	(1,893)	(742)
Investments, Fair Value	256,185	279,073
Collateralized Corporate Bank Loans [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	137,713	125,536
Investments, Gross Unrealized Gains	827	702
Investments, Gross Unrealized Losses	(133)	(301)
Investments, Fair Value	138,407	125,937
Municipal Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	135,256	134,052
Investments, Gross Unrealized Gains	2,753	709
Investments, Gross Unrealized Losses	(821)	(505)
Investments, Fair Value	137,188	134,256
Mortgage Backed [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	15,019	16,712
Investments, Gross Unrealized Gains	28	37
Investments, Gross Unrealized Losses	(399)	(216)
Investments, Fair Value	$ 14,648	$ 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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