Investments (Amortized Cost and Estimated Fair Value of Investments in Debt and Equity Securities by Category) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Investments, Amortized Cost	$ 495,096	$ 476,130
Investments, Gross Unrealized Gains	42,178	35,076
Investments, Gross Unrealized Losses	(4,751)	(3,977)
Investments, Fair Value	532,523us-gaap_Investments	507,229us-gaap_Investments
Equity Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	28,120	25,360
Investments, Gross Unrealized Gains	37,646	31,086
Investments, Gross Unrealized Losses	(300)	(2)
Investments, Fair Value	65,466	56,444
Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	466,976	450,770
Investments, Gross Unrealized Gains	4,532	3,990
Investments, Gross Unrealized Losses	(4,451)	(3,975)
Investments, Fair Value	467,057	450,785
US Treasury Securities and Obligations of U.S. Government [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	92,292	93,280
Investments, Gross Unrealized Gains	383	29
Investments, Gross Unrealized Losses		(4)
Investments, Fair Value	92,675	93,305
Corporate Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	31,093	28,643
Investments, Gross Unrealized Gains	824	884
Investments, Gross Unrealized Losses	(59)	(85)
Investments, Fair Value	31,858	29,442
Collateralized Corporate Bank Loans [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	114,385	115,358
Investments, Gross Unrealized Gains	572	206
Investments, Gross Unrealized Losses	(2,068)	(1,915)
Investments, Fair Value	112,889	113,649
Municipal Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	162,088	161,546
Investments, Gross Unrealized Gains	2,362	2,384
Investments, Gross Unrealized Losses	(2,239)	(1,601)
Investments, Fair Value	162,211	162,329
Mortgage Backed [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	67,118	51,943
Investments, Gross Unrealized Gains	391	487
Investments, Gross Unrealized Losses	(85)	(370)
Investments, Fair Value	$ 67,424	$ 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

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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

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

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

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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

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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