Federal Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
DEFERRED TAX ASSETS
Invested assets, principally due to impairment losses	$ 18,148	$ 23,570
Investment in real estate and other invested assets, principally due to investment valuation allowances	8,424	8,547
Policyholder funds, principally due to policy reserve discount	91,362	90,480
Policyholder funds, principally due to unearned premium reserve	24,586	23,001
Participating policyholders’ surplus	32,785	34,538
Pension	3,598	26,274
Commissions and other expenses	3,108	3,796
Other assets	9,756	15,745
Tax carryforwards	138	60
Gross deferred tax assets before valuation allowance	191,905	226,011
Valuation allowance	(2,700)	0
Gross deferred tax assets after valuation allowance	189,205	226,011
DEFERRED TAX LIABILITIES
Marketable securities, principally due to net unrealized gains	161,256	253,526
Investment in bonds, principally due to differences between GAAP and tax basis	13,088	12,547
Deferred policy acquisition costs, due to difference between GAAP and tax amortization methods	240,731	220,809
Property, plant and equipment, principally due to difference between GAAP and tax depreciation methods	22,204	19,203
Other liabilities	16,111	36,296
Gross deferred tax liabilities	453,390	542,381
Total net deferred tax liability	$ 264,185	$ 316,370