Investments (Amortized Cost and Estimated Fair Value of Investments in Debt and Equity Securities by Category) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Investments, Amortized Cost	$ 596,217	$ 622,740
Investments, Gross Unrealized Gains	27,777	24,959
Investments, Gross Unrealized Losses	(11,177)	(19,785)
Investments, Fair Value	612,817	627,914
Other Investments [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	3,763	3,763
Investments, Gross Unrealized Losses	(2,579)	(2,615)
Investments, Fair Value	1,184	1,148
Equity Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	68,709	68,709
Investments, Gross Unrealized Gains	25,549	20,693
Investments, Gross Unrealized Losses	(5,602)	(8,506)
Investments, Fair Value	88,656	80,896
Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	523,745	550,268
Investments, Gross Unrealized Gains	2,228	4,266
Investments, Gross Unrealized Losses	(2,996)	(8,664)
Investments, Fair Value	522,977	545,870
U.S. Treasury Securities and Obligations of U.S. Government [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	48,490	48,609
Investments, Gross Unrealized Gains	7	5
Investments, Gross Unrealized Losses	(288)	(508)
Investments, Fair Value	48,209	48,106
Corporate Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	217,979	243,314
Investments, Gross Unrealized Gains	1,296	440
Investments, Gross Unrealized Losses	(440)	(1,602)
Investments, Fair Value	218,835	242,152
Collateralized Corporate Bank Loans [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	130,526	131,779
Investments, Gross Unrealized Gains	66	19
Investments, Gross Unrealized Losses	(1,752)	(5,270)
Investments, Fair Value	128,840	126,528
Municipal Bonds [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	113,812	112,574
Investments, Gross Unrealized Gains	845	3,791
Investments, Gross Unrealized Losses	(298)	(838)
Investments, Fair Value	114,359	115,527
Mortgage Backed [Member] \| Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	12,938	13,992
Investments, Gross Unrealized Gains	14	11
Investments, Gross Unrealized Losses	(218)	(446)
Investments, Fair Value	$ 12,734	$ 13,557

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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