Investments in Equity Securities (Investments in Equity Securities Available for Sale) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Fair Value
Debt Securities, Available-for-sale [Line Items]
Cost	$ 516,014	$ 345,099
Gross unrealized gains	124,323	165,210
Gross unrealized losses	(14,670)	(29,689)
Equity securities	625,667	480,620
Fair Value \| Common stocks
Debt Securities, Available-for-sale [Line Items]
Cost	335,617	175,928
Gross unrealized gains	28,742	16,967
Gross unrealized losses	(14,178)	(26,090)
Equity securities	350,181	166,805
Fair Value \| Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Cost	180,397	169,171
Gross unrealized gains	95,581	148,243
Gross unrealized losses	(492)	(3,599)
Equity securities	275,486	313,815
Carrying Value
Debt Securities, Available-for-sale [Line Items]
Equity securities	625,667	480,620
Carrying Value \| Common stocks
Debt Securities, Available-for-sale [Line Items]
Equity securities	350,181	166,805
Carrying Value \| Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 275,486	$ 313,815

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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Amount of unrealized gain on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714

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Amount of unrealized loss on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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