Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($)	Dec. 31, 2016 segment	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Number of reportable segments | segment	4
Significant of Account Policies [Line Items]
Concentration risk percentage	100.00%
Number of operating segments sold | segment					1
Capital called from investment funds	$ 227,000
Investment funds, unfunded commitments	$ 435,000
Percentage of investment securities not classified as corporate securities, state and municipal securities, redeemable preferred stocks and U.S. government securities (less than)	1.00%
Fair value determined by third party	97.00%
Shareholders' equity	$ 8,771,092	$ 7,294,307		$ 5,415,177		$ 6,231,421
Commercial mortgage loan participations	546,981	326,347
Agent debit balances	456,000	423,877
Agent debit balances, allowance for credit losses	1,200
Advertising costs charged to earnings and included in other operating	9,800	9,500		9,000
Capitalized advertising costs	1,400,000	1,300,000
Carrying value of investment in low-income housing interests	306,000	206,000
Obligations under future commitments for low-income housing interests	162,000
Original cost of property and equipment	350,000	298,000
Accumulated depreciation	164,000	137,000
Depreciation expense	$ 17,000	16,000		13,000
Traditional life and health, interest rate, low end	2.50%
Traditional life and health, interest rate, high end	7.00%
Traditional life and health, weighted average interest rate	5.70%
Insurance policy charges	$ 14,700	15,600		16,400
Commercial loan participations
Significant of Account Policies [Line Items]
Financing receivable, term	3 years
Financing receivable, extension term	2 years
Commercial loan participations, unfunded loan commitment
Significant of Account Policies [Line Items]
Carrying value, net of valuation allowance	$ 47,000
Commercial mortgage participations
Significant of Account Policies [Line Items]
Carrying value, net of valuation allowance	160,602	137,692
Commercial mortgage loan participations	160,602	137,692
Accrued interest receivable	433
Investment in limited partnerships
Significant of Account Policies [Line Items]
Investment funds, unfunded commitments	435,002
Retained Earnings
Significant of Account Policies [Line Items]
Shareholders' equity	$ 5,874,109	5,551,329		5,213,468		4,806,208
Cumulative Effect, Period Of Adoption, Adjustment
Significant of Account Policies [Line Items]
Shareholders' equity		(454)	[1]	(392)		4,896
Agent debit balances		(240)
Cumulative Effect, Period Of Adoption, Adjustment | Commercial mortgage participations
Significant of Account Policies [Line Items]
Commercial mortgage loan participations		(335)
Cumulative Effect, Period Of Adoption, Adjustment | Retained Earnings
Significant of Account Policies [Line Items]
Shareholders' equity		(454)	[1]	(392)		4,896
Cumulative Effect, Period Of Adoption, Adjustment | Retained Earnings | Accounting Standards Update 2016-13, Adjustment for Commercial Loan Participations
Significant of Account Policies [Line Items]
Shareholders' equity		(265)
Cumulative Effect, Period Of Adoption, Adjustment | Retained Earnings | Accounting Standards Update 2016-13, Adjustment for Agent Debit Balances
Significant of Account Policies [Line Items]
Shareholders' equity		(189)
Cumulative Effect, Period Of Adoption, Adjusted Balance
Significant of Account Policies [Line Items]
Shareholders' equity		7,293,853		5,414,785		6,236,317
Agent debit balances		423,637
Cumulative Effect, Period Of Adoption, Adjusted Balance | Commercial mortgage participations
Significant of Account Policies [Line Items]
Commercial mortgage loan participations		137,357
Cumulative Effect, Period Of Adoption, Adjusted Balance | Retained Earnings
Significant of Account Policies [Line Items]
Shareholders' equity		$ 5,550,875		$ 5,213,076		$ 4,811,104
Equity Option | Torchmark Corporation 2018 Incentive Plan
Significant of Account Policies [Line Items]
Term over which monthly data points are used to derive volatility	3 years
Equity Option | Employee | Three Year Vesting Period | Torchmark Corporation 2018 Incentive Plan
Significant of Account Policies [Line Items]
Option grants contractual term	7 years
Vesting period	3 years
Equity Option | Employee | Five Year Vesting Period | Torchmark Corporation 2018 Incentive Plan
Significant of Account Policies [Line Items]
Option grants contractual term	10 years
Vesting period	5 years
Equity Option | Director | Torchmark Corporation 2018 Incentive Plan
Significant of Account Policies [Line Items]
Vesting period	6 months
Low-income housing credits and certain limited partnerships
Significant of Account Policies [Line Items]
Concentration risk percentage	1.00%
Life insurance
Significant of Account Policies [Line Items]
Proportion of future policy reserves which are not universal life type	90.00%
Minimum | Investment in limited partnerships
Significant of Account Policies [Line Items]
Investment funds ownership percentage	1.00%
Maximum | Investment in limited partnerships
Significant of Account Policies [Line Items]
Investment funds ownership percentage	20.00%
Equipment | Minimum
Significant of Account Policies [Line Items]
Property and equipment, estimated useful life	3 years
Equipment | Maximum
Significant of Account Policies [Line Items]
Property and equipment, estimated useful life	10 years
Building and Improvements | Minimum
Significant of Account Policies [Line Items]
Property and equipment, estimated useful life	15 years
Building and Improvements | Maximum
Significant of Account Policies [Line Items]
Property and equipment, estimated useful life	40 years

[1] Adoption of Accounting Standard Update (ASU) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, on January 1, 2020. See further discussion in Note 1—Significant Accounting Policies.