Summary of Significant Accounting Policies and Practices - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Significant Accounting Policies [Line Items]
Interest due on loan cease to accrue, number of days past due	90 days
Number of years property held for sale	1 year
Delinquent coupon payments	$ 0
Percentage of participating policy of life insurance in-force	4.50%
Percentage of participating policy of life premium	17.20%
Income tax expense (benefit) from tax reform			$ 206,400,000
Largest amount of tax benefit, percent	50.00%
Farm Family Life
Schedule Of Significant Accounting Policies [Line Items]
Percentage of profit on participating business, stockholders' share of profits	10.00%
Dividends to participating policyholders	$ 8,400,000	$ 7,600,000	6,100,000
Additional income allocated to participating policyholders	34,000,000.0	$ 4,200,000	$ 16,200,000
Share of profit on participating business, face amount of participating life insurance in-force	$ 0.50
Minimum
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful life of real estate investment	15 years
Estimated useful lives	3 years
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Entity ownership percentage	100.00%
Estimated useful life of real estate investment	50 years
Estimated useful lives	50 years