Investments (Amortized Cost and Estimated Fair Value of Investments in Debt and Equity Securities by Category) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Investments, Amortized Cost	$ 549,865	$ 476,130
Investments, Gross Unrealized Gains	27,689	35,076
Investments, Gross Unrealized Losses	(10,162)	(3,977)
Investments, Fair Value	567,392	507,229
Equity Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	24,957	25,360
Investments, Gross Unrealized Gains	23,998	31,086
Investments, Gross Unrealized Losses	(726)	(2)
Investments, Fair Value	48,229	56,444
Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	524,908	450,770
Investments, Gross Unrealized Gains	3,691	3,990
Investments, Gross Unrealized Losses	(9,436)	(3,975)
Investments, Fair Value	519,163	450,785
US Treasury Securities and Obligations of U.S. Government [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	91,311	93,280
Investments, Gross Unrealized Gains	370	29
Investments, Gross Unrealized Losses		(4)
Investments, Fair Value	91,681	93,305
Corporate Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	50,638	28,643
Investments, Gross Unrealized Gains	586	884
Investments, Gross Unrealized Losses	(614)	(85)
Investments, Fair Value	50,610	29,442
Collateralized Corporate Bank Loans [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	124,158	115,358
Investments, Gross Unrealized Gains	344	206
Investments, Gross Unrealized Losses	(2,368)	(1,915)
Investments, Fair Value	122,134	113,649
Municipal Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	196,174	161,546
Investments, Gross Unrealized Gains	2,108	2,384
Investments, Gross Unrealized Losses	(6,334)	(1,601)
Investments, Fair Value	191,948	162,329
Mortgage Backed [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	62,627	51,943
Investments, Gross Unrealized Gains	283	487
Investments, Gross Unrealized Losses	(120)	(370)
Investments, Fair Value	$ 62,790	$ 52,060

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.

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)

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

+ 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 (b)

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 50

-Paragraph 2

-Subparagraph (c)

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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

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