Investments - Schedule of Unrealized Investment Losses by Class of Investment (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 192,313	$ 4,698,830
Unrealized Loss	(3,188)	(252,192)
Fair Value	1,154,336	1,290,990
Unrealized Loss	(106,142)	(176,187)
Fair Value	1,346,649	5,989,820
Total	109,330	428,379
Investment Grade
Debt Securities, Available-for-sale [Line Items]
Fair Value	135,740	4,458,883
Unrealized Loss	(237)	(229,105)
Fair Value	880,078	1,091,128
Unrealized Loss	(32,406)	(106,067)
Fair Value	1,015,818	5,550,011
Total	32,643	335,172
Investment Grade \| U.S. Government direct, guaranteed, and government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Fair Value	2	37,182
Unrealized Loss	0	(212)
Fair Value	28,896	89,664
Unrealized Loss	(420)	(2,575)
Fair Value	28,898	126,846
Total	420	2,787
Investment Grade \| States, municipalities, and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value	29,960	124,907
Unrealized Loss	(40)	(1,648)
Fair Value	0	7,981
Unrealized Loss	0	(102)
Fair Value	29,960	132,888
Total	40	1,750
Investment Grade \| Foreign governments
Debt Securities, Available-for-sale [Line Items]
Fair Value	0
Unrealized Loss	0
Fair Value	0
Unrealized Loss	0
Fair Value	0
Total	0
Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	105,716	4,252,191
Unrealized Loss	(197)	(226,611)
Fair Value	851,182	993,483
Unrealized Loss	(31,986)	(103,390)
Fair Value	956,898	5,245,674
Total	32,183	330,001
Investment Grade \| Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	62	44,603
Unrealized Loss	0	(634)
Fair Value	0	0
Unrealized Loss	0	0
Fair Value	62	44,603
Total	0	634
Below Investment Grade
Debt Securities, Available-for-sale [Line Items]
Fair Value	56,573	239,947
Unrealized Loss	(2,951)	(23,087)
Fair Value	274,258	199,862
Unrealized Loss	(73,736)	(70,120)
Fair Value	330,831	439,809
Total	76,687	93,207
Below Investment Grade \| States, municipalities, and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value	82
Unrealized Loss	(138)
Fair Value	0
Unrealized Loss	0
Fair Value	82
Total	138
Below Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	42,387	239,947
Unrealized Loss	(2,517)	(23,087)
Fair Value	260,755	186,276
Unrealized Loss	(67,239)	(63,706)
Fair Value	303,142	426,223
Total	69,756	86,793
Below Investment Grade \| Collateralized debt obligations
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
Unrealized Loss	0	0
Fair Value	13,503	13,586
Unrealized Loss	(6,497)	(6,414)
Fair Value	13,503	13,586
Total	6,497	6,414
Below Investment Grade \| Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	14,104
Unrealized Loss	(296)
Fair Value	0
Unrealized Loss	0
Fair Value	14,104
Total	296
Financial \| Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	74,915	931,161
Unrealized Loss	(85)	(36,337)
Fair Value	130,430	241,442
Unrealized Loss	(4,854)	(21,572)
Fair Value	205,345	1,172,603
Total	4,939	57,909
Financial \| Below Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	7,379	22,087
Unrealized Loss	(450)	(8,674)
Fair Value	122,459	81,101
Unrealized Loss	(25,082)	(20,932)
Fair Value	129,838	103,188
Total	25,532	29,606
Utilities \| Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	329,753
Unrealized Loss	0	(11,680)
Fair Value	73,863	121,308
Unrealized Loss	(1,126)	(9,442)
Fair Value	73,863	451,061
Total	1,126	21,122
Utilities \| Below Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	15,449	28,613
Unrealized Loss	(1,136)	(3,277)
Fair Value	12,300	0
Unrealized Loss	(3,949)	0
Fair Value	27,749	28,613
Total	5,085	3,277
Energy \| Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	6,198	475,736
Unrealized Loss	(80)	(29,426)
Fair Value	65,067	54,937
Unrealized Loss	(6,781)	(9,382)
Fair Value	71,265	530,673
Total	6,861	38,808
Energy \| Below Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,872	42,874
Unrealized Loss	(346)	(3,901)
Fair Value	44,046	36,122
Unrealized Loss	(21,656)	(19,662)
Fair Value	46,918	78,996
Total	22,002	23,563
Other corporate sectors \| Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	24,603	2,515,541
Unrealized Loss	(32)	(149,168)
Fair Value	581,822	575,796
Unrealized Loss	(19,225)	(62,994)
Fair Value	606,425	3,091,337
Total	19,257	212,162
Other corporate sectors \| Below Investment Grade \| Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value	16,687	146,373
Unrealized Loss	(585)	(7,235)
Fair Value	81,950	69,053
Unrealized Loss	(16,552)	(23,112)
Fair Value	98,637	215,426
Total	$ 17,137	$ 30,347

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922890-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922890-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ExternalCreditRatingByGroupingAxis=us-gaap_ExternalCreditRatingInvestmentGradeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=gl_USGovernmentDirectGuaranteedAndGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=gl_OtherAssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ExternalCreditRatingByGroupingAxis=us-gaap_ExternalCreditRatingNonInvestmentGradeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CollateralizedDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentSectorAxis=gl_FinancialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentSectorAxis=gl_UtilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentSectorAxis=gl_EnergyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentSectorAxis=gl_OtherCorporateSectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: