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Federal Income Taxes (Reconciliation of Federal Income Tax on Income at the Corporate Rate to the Effective Tax Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Provisional Increase to Deferred Tax Asset	$ 7,500
Tax at statutory rate of 35%	91,689	$ 76,984	$ 81,442
Tax-advantaged interest	(11,510)	(12,126)	(13,164)
Dividends received deduction	(1,961)	(1,114)	(1,817)
Share-based compensation expense income tax benefit	(4,281)	0	0
Tax Reform Deferred Tax Asset Impact	20,205	0	0
Tax Benefit on Unrealized Gains	5,700
Other	(1,000)	(2,284)	370
Total federal income tax expense	$ 93,142	$ 61,460	$ 66,831

X

- Definition

The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to investment income that is tax advantaged. Tax advantaged investment securities generally are, by statute, tax-reduced, tax-deferred, or tax-free.

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Provisional Increase to Deferred Tax Asset due to the change in approach from the Tax Cuts and Jobs Act.

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Tax Benefit on Unrealized Gains

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The amount of adjustment to stockholders' equity associated with an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Section S99
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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for dividend.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other adjustments.

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