XML 148 R60.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2

Investments (Number of Securities in an Unrealized Unrecognized Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Percentage Decline in Fair Value Percentage of Amortized Cost	1.00%	2.00%
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	$ 100	$ 200
Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	516,259	2,142,433
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3,379)	(36,948)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	230,770	275,174
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(4,359)	(8,119)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	747,029	2,417,607
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(7,738)	(45,067)
U.S. Government and Government Agencies [Member] | Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		6,693
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(174)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		23,163
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(418)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value		29,856
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		(592)
Foreign Government [Member] | Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,416	12,208
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)	(93)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	1,482
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(14)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	1,416	13,690
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(2)	(107)
Obligations of States and Political Subdivisions [Member] | Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	35,838	196,798
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(270)	(2,074)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	42,821
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(557)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	35,838	239,619
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(270)	(2,631)
Corporate Securities [Member] | Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	84,832	1,041,952
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(480)	(23,649)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	20,182	78,953
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(830)	(4,316)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	105,014	1,120,905
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,310)	(27,965)
Collateralized Loan Obligations and Other Asset-Backed Securities [Member] | Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	205,191	516,106
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,938)	(6,750)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	204,385	16,800
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(3,496)	(193)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	409,576	532,906
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(5,434)	(6,943)
Commercial Mortgage Backed Securities [Member] | Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	62,893	229,338
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(264)	(2,548)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	828	66,294
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(3)	(1,200)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	63,721	295,632
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(267)	(3,748)
Residential Mortgage Backed Securities [Member] | Available-for-sale Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	126,089	139,338
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(425)	(1,660)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5,375	45,661
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(30)	(1,421)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	131,464	184,999
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (455)	$ (3,081)

X

- Definition

This item represents the percentage decline in fair value of fixed maturity securities compared to amortized cost that are in a loss position. This impairment has been determined to be temporary.

+ References

No definition available.

+ Details

Name:	sigi_PercentageDeclineInFairValuePercentage
Namespace Prefix:	sigi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

This item represents the sum of (i) the excess of amortized cost over fair value for held-to-maturity securities that are in a loss position and (ii) the market fluctuations on held-to-maturity securities from the later of (a) the date a security is designated as held-to-maturity; or (b) the date that an other-than-temporary impairment charge is recognized on a held-to-maturity security for securities that are in an unrecognized loss position.

+ References

No definition available.

+ Details

Name:	sigi_UnrealizedUnrecognizedLoss
Namespace Prefix:	sigi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

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

X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

No definition available.

+ Details

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

X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.

+ References

No definition available.

+ Details

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

X

- Details

Name:	sigi_ScheduleOfFairValueAndGrossPreTaxUnrealizedUnrecognizedLossOfSecuritiesByLengthOfTimeAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: