Federal Income Taxes - Effective Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income tax expense before tax on equity in earnings of unconsolidated affiliates	$ 17,717	$ 38,486	$ 99,323	$ 64,118
Tax on equity in earnings of unconsolidated affiliates	9,465	2,736	21,488	3,970
Total expected income tax expense at the statutory rate	27,182	41,222	120,811	68,088
Tax-exempt investment income	(1,027)	(830)	(2,945)	(2,509)
Deferred tax change	0	0	0	(909)
Dividend exclusion	(817)	(1,064)	(2,598)	(3,050)
Miscellaneous tax credits, net	(1,521)	(1,252)	(6,512)	(5,994)
Low income housing tax credit expense	1,324	1,251	4,265	3,755
Noncontrolling interest	(2,284)	0	(2,284)	0
Change in valuation allowance	70	0	235	2,700
Tax accrual adjustment	0	(2,893)	0	(2,893)
Return to provision	0	(18,332)	0	(18,332)
Other items, net	(452)	1,117	828	1,509
Provision for federal income taxes	$ 22,475	$ 19,219	$ 111,800	$ 42,365
Income tax expense before tax on equity in earnings of unconsolidated affiliates, percentage	13.70%	20.00%	17.30%	19.80%
Tax on equity in earnings of unconsolidated affiliates, percentage	7.30%	1.00%	3.70%	1.20%
Total expected income tax expense at the statutory rate, percentage	21.00%	21.00%	21.00%	21.00%
Tax-exempt investment income, percentage	(0.80%)	(0.40%)	(0.50%)	(0.80%)
Deferred tax change, percentage	0.00%	0.00%	0.00%	(0.30%)
Dividend exclusion, percentage	(0.60%)	(0.50%)	(0.40%)	(0.90%)
Miscellaneous tax credits, net, percentage	(1.20%)	(0.60%)	(1.10%)	(1.80%)
Low income housing tax credit expense, percentage	1.00%	0.60%	0.70%	1.20%
Noncontrolling interest, percentage	(1.80%)	0.00%	(0.40%)	0.00%
Change in valuation allowance, percentage	0.10%	0.00%	0.00%	0.80%
Tax accrual adjustment, percentage	0.00%	(1.50%)	0.00%	(0.90%)
Return to provision, percentage	0.00%	(9.30%)	0.00%	(5.70%)
Other items, net, percentage	(0.30%)	0.80%	0.10%	0.50%
Provision for federal income tax before interest expense, percentage	17.40%	10.10%	19.40%	13.10%

Effective income tax rate reconciliation deferred tax adjustments including tax reform.

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Effective Income Tax Rate Reconciliation On Income Before Tax On Equity In Earnings Of Unconsolidated Affiliates

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The percentage of the difference between total income tax expense or benefit 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 low income housing credits.

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The portion of the difference between total income tax expense or benefit 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 low income housing credits.

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