Investments (Amortized Cost and Estimated Fair Value of Investments in Debt and Equity Securities by Category) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Investments, Amortized Cost	$ 647,329	$ 632,996
Investments, Gross Unrealized Gains	26,120	25,992
Investments, Gross Unrealized Losses	(3,195)	(4,869)
Investments, Fair Value	670,254	654,119
Other Investments [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	3,763	3,763
Investments, Gross Unrealized Gains	458	1,188
Investments, Fair Value	4,221	4,951
Equity Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	26,681	31,449
Investments, Gross Unrealized Gains	22,237	21,052
Investments, Gross Unrealized Losses	(1,119)	(790)
Investments, Fair Value	47,799	51,711
Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	616,885	597,784
Investments, Gross Unrealized Gains	3,425	3,752
Investments, Gross Unrealized Losses	(2,076)	(4,079)
Investments, Fair Value	618,234	597,457
Us Treasury Securities and Obligations of U.S. Government [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	42,034	41,976
Investments, Gross Unrealized Gains	6	66
Investments, Gross Unrealized Losses	(6)	(20)
Investments, Fair Value	42,034	42,022
Corporate Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	283,851	224,915
Investments, Gross Unrealized Gains	1,810	1,722
Investments, Gross Unrealized Losses	(1,040)	(575)
Investments, Fair Value	284,621	226,062
Collateralized Corporate Bank Loans [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	123,070	105,220
Investments, Gross Unrealized Gains	628	959
Investments, Gross Unrealized Losses	(455)	(170)
Investments, Fair Value	123,243	106,009
Municipal Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	148,473	165,900
Investments, Gross Unrealized Gains	917	956
Investments, Gross Unrealized Losses	(407)	(2,961)
Investments, Fair Value	148,983	163,895
Mortgage Backed [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	19,457	59,773
Investments, Gross Unrealized Gains	64	49
Investments, Gross Unrealized Losses	(168)	(353)
Investments, Fair Value	$ 19,353	$ 59,469

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=73527792&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=73527792&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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