XML 395 R30.htm IDEA: XBRL DOCUMENT v3.21.2

Investment Securities (Tables)

9 Months Ended

Sep. 30, 2021

Investments, Debt and Equity Securities [Abstract]

Pre-tax net investment income

The following table presents pre-tax net investment income for the three and nine months ended September 30, 2021 and 2020:

						Three Months Ended												Nine Months Ended
						September 30,												September 30,
Millions						2021						2020						2021						2020
Fixed maturity investments						$	8.2					$	7.0					$	21.9					$	22.4
Short-term investments						—						.1						.5						1.0
Common equity securities						.1						.5						.1						6.5
Investment in MediaAlpha						—						55.0						—						60.0
Other long-term investments						12.0						8.9						37.1						24.7
Amount attributable to TPC Providers						(.2)						—						(.8)						—
Total investment income						20.1						71.5						58.8						114.6
Third-party investment expenses						(.6)						(.3)						(1.6)						(.9)
Net investment income, pre-tax						$	19.5					$	71.2					$	57.2					$	113.7

Schedule of net realized and unrealized investment gains and losses

The following table presents net realized and unrealized investment gains (losses) for the three and nine months ended September 30, 2021 and 2020:

									Three Months Ended												Nine Months Ended
									September 30,												September 30,
Millions									2021						2020						2021						2020
Fixed maturity investments									$	(6.8)					$	3.6					$	(23.2)					$	35.8
Short-term investments									(.3)						—						—						.4
Common equity securities									1.6						48.4						7.7						5.9
Investment in MediaAlpha									(396.8)						250.0						(325.5)						295.0
Other long-term investments									37.7						4.6						113.2						(34.3)
Amount attributable to TPC Providers									(1.7)						—						(6.5)						—
Net realized and unrealized investment (losses) gains(1)									(366.3)						306.6						(234.3)						302.8
Less: net (losses) gains on investment securities sold during the period									(4.8)						36.1						(5.1)						29.6
Net realized and unrealized investment (losses) gains on investment securities held at the end of the period									$	(361.5)					$	270.5					$	(229.2)					$	273.2

(1) For the three months ended September 30, 2021 and 2020, includes $(7.0) and $0.8 of realized and unrealized investment gains (losses) related to foreign currency exchange. For the nine months ended September 30, 2021 and 2020, includes $(7.4) and $(0.8) of realized and unrealized investment gains (losses) related to foreign currency exchange.

Net unrealized investment gains (losses) for Level 3 investments

The following table presents total gains included in earnings attributable to net unrealized investment gains for Level 3 investments for the three and nine months ended September 30, 2021 and 2020 for investments still held at the end of the period:

						Three Months Ended															Nine Months Ended
						September 30,															September 30,
Millions						2021						2020									2021						2020
Other long-term investments						$	26.5					$	260.1								$	75.5					$	276.0
Total net unrealized investment gains, pre-tax - Level 3 investments						$	26.5					$	260.1								$	75.5					$	276.0

Investment holdings, equity securities, convertible fixed maturities and other long-term investments

The following tables present the cost or amortized cost, gross unrealized investment gains (losses) and carrying values of White Mountains’s fixed maturity investments as of September 30, 2021 and December 31, 2020:

						September 30, 2021
Millions						Cost or Amortized Cost						Gross Unrealized Gains						Gross Unrealized Losses						Net Foreign Currency Gains (Losses)						Carrying Value
U.S. Government and agency obligations						$	207.4					$	.8					$	(.6)					$	—					$	207.6
Debt securities issued by corporations						945.2						13.1						(3.4)						(.7)						954.2
Municipal obligations						276.1						18.0						(.7)						—						293.4
Mortgage and asset-backed securities						247.3						4.2						(1.4)						—						250.1
Collateralized loan obligations						128.5						—						(.4)						(.5)						127.6
Total fixed maturity investments						$	1,804.5					$	36.1					$	(6.5)					$	(1.2)					$	1,832.9

						December 31, 2020
Millions						Cost or Amortized Cost						Gross Unrealized Gains						Gross Unrealized Gains (Losses)												Carrying Value
U.S. Government and agency obligations						$	173.2					$	3.1					$	—											$	176.3
Debt securities issued by corporations						522.8						24.7						(.1)												547.4
Municipal obligations						244.0						21.0						—												265.0
Mortgage and asset-backed securities						211.7						6.8						—												218.5
Total fixed maturity investments						$	1,151.7					$	55.6					$	(.1)											$	1,207.2

The following tables present the cost or amortized cost, gross unrealized investment gains (losses), net foreign currency gains (losses), and carrying values of common equity securities, White Mountains’s investment in MediaAlpha and other long-term investments as of September 30, 2021 and December 31, 2020:

						September 30, 2021
Millions						Cost or Amortized Cost						Gross Unrealized Gains						Gross Unrealized Losses						Net Foreign Currency Gains (Losses)						Carrying Value
Common equity securities						$	152.5					$	8.8					$	(.5)					$	(1.2)					$	159.6
Investment in MediaAlpha						$	—					$	316.4					$	—					$	—					$	316.4
Other long-term investments						$	1,154.7					$	197.6					$	(62.9)					$	(3.9)					$	1,285.5

						December 31, 2020
Millions						Cost or Amortized Cost						Gross Unrealized Gains						Gross Unrealized Losses						Net Foreign Currency Gains (Losses)						Carrying Value
Investment in MediaAlpha						$	—					$	802.2					$	—					$	—					$	802.2
Other long-term investments						$	767.4					$	95.8					$	(78.1)					$	1.7					$	786.8

Schedule of fixed maturity investment holdings

The following table presents the cost or amortized cost and carrying value of White Mountains’s fixed maturity investments by contractual maturity as of September 30, 2021. Actual maturities could differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties.

						September 30, 2021
Millions						Cost or Amortized Cost						Carrying Value
Due in one year or less						$	111.9					$	112.7
Due after one year through five years						836.1						843.4
Due after five years through ten years						368.5						377.3
Due after ten years						112.2						121.8
Mortgage and asset-backed securities and collateralized loan obligations						375.8						377.7
Total fixed maturity investments						$	1,804.5					$	1,832.9

Fair value measurements by level, investment securities

The following tables present White Mountains’s fair value measurements for investments as of September 30, 2021 and December 31, 2020 by level. The major security types were based on the legal form of the securities. White Mountains has disaggregated its fixed maturity investments based on the issuing entity type, which impacts credit quality, with debt securities issued by U.S. government entities carrying minimal credit risk, while the credit and other risks associated with other issuers, such as corporations, municipalities or entities issuing mortgage and asset-backed securities vary depending on the nature of the issuing entity type. White Mountains further disaggregates debt securities issued by corporations by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated this asset class into subclasses based on the similar sectors and industry classifications it uses to evaluate investment risk and performance against commonly used benchmarks, such as the Bloomberg Barclays U.S. Intermediate Aggregate.

						September 30, 2021
Millions						Fair Value						Level 1						Level 2						Level 3
Fixed maturity investments:
U.S. Government and agency obligations						$	207.6					$	207.6					$	—					$	—
Debt securities issued by corporations:
Financials						246.5						—						246.5						—
Consumer						180.5						—						180.5						—
Industrial						114.8						—						114.8						—
Technology						110.8						—						110.8						—
Healthcare						98.2						—						98.2						—
Utilities						69.9						—						69.9						—
Communications						53.2						—						53.2						—
Energy						47.0						—						47.0						—
Materials						33.3						—						33.3						—
Total debt securities issued by corporations						954.2						—						954.2						—
Municipal obligations						293.4						—						293.4						—
Mortgage and asset-backed securities						250.1						—						250.1						—
Collateralized loan obligations						127.6						—						127.6						—
Total fixed maturity investments						1,832.9						207.6						1,625.3						—
Short-term investments						609.5						601.6						7.9						—
Common equity securities (1)						159.6						—						159.6						—
Investment in MediaAlpha						316.4						316.4						—						—
Other long-term investments						814.5						—						—						814.5
Other long-term investments — NAV (2)						471.0						—						—						—
Total other long-term investments						1,285.5						—						—						814.5
Total investments						$	4,203.9					$	1,125.6					$	1,792.8					$	814.5

(1) Consist of investments in listed funds that predominantly invest in international equities.

(2) Consists of private equity funds, a hedge fund, Lloyd’s trust deposits, a bank loan fund and ILS funds for which fair value is measured at NAV using the practical expedient. Investments for which fair value is measured at NAV are not classified within the fair value hierarchy.

						December 31, 2020
Millions						Fair Value						Level 1						Level 2						Level 3
Fixed maturity investments:
U.S. Government and agency obligations						$	176.3					$	176.3					$	—					$	—
Debt securities issued by corporations:
Financials						133.9						—						133.9						—
Consumer						81.9						—						81.9						—
Industrial						66.9						—						66.9						—
Technology						66.7						—						66.7						—
Healthcare						51.5						—						51.5						—
Communications						44.5						—						44.5						—
Energy						35.8						—						35.8						—
Materials						33.9						—						33.9						—
Utilities						32.3						—						32.3						—
Total debt securities issued by corporations						547.4						—						547.4						—
Municipal obligations						265.0						—						265.0						—
Mortgage and asset-backed securities						218.5						—						218.5						—
Total fixed maturity investments						1,207.2						176.3						1,030.9						—
Short-term investments						142.9						142.9						—						—
Investment in MediaAlpha						802.2						802.2						—						—
Other long-term investments						614.2						—						—						614.2
Other long-term investments — NAV (1)						172.6						—						—						—
Total other long-term investments						786.8						—						—						614.2
Total investments						$	2,939.1					$	1,121.4					$	1,030.9					$	614.2

(1) Consists of private equity funds and ILS funds for which fair value is measured at NAV using the practical expedient. Investments for which fair value is measured at NAV are not classified within the fair value hierarchy.

Debt securities issued by corporations, credit ratings

The following table presents the credit ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of September 30, 2021 and December 31, 2020:

						Fair Value at
Millions						September 30, 2021						December 31, 2020
AAA						$	12.7					$	10.6
AA						85.7						57.9
A						473.3						318.3
BBB						373.7						159.6
BB						—						1.0
Other						8.8						—
Debt securities issued by corporations (1)						$	954.2					$	547.4

(1)    Credit ratings are based upon issuer credit ratings provided by Standard & Poor’s Financial Services LLC (“Standard & Poor’s”), or if unrated by Standard & Poor’s, long-term obligation ratings provided by Moody’s Investor Service, Inc.

Mortgage-backed, asset-backed securities

The following table presents the fair value of White Mountains’s mortgage and asset-backed securities and collateralized loan obligations as of September 30, 2021 and December 31, 2020:

						September 30, 2021																		December 31, 2020
Millions						Fair Value						Level 2						Level 3						Fair Value						Level 2						Level 3
Mortgage-backed securities:
Agency:
FNMA						$	125.3					$	125.3					$	—					$	88.7					$	88.7					$	—
FHLMC						76.5						76.5						—						70.1						70.1						—
GNMA						29.4						29.4						—						40.6						40.6						—
Total agency (1)						231.2						231.2						—						199.4						199.4						—
Non-agency: Residential						.6						.6						—						—						—						—
Total non-agency						.6						.6						—						—						—						—
Total mortgage-backed securities						231.8						231.8						—						199.4						199.4						—
Other asset-backed securities:
Credit card receivables						11.2						11.2						—						11.3						11.3						—
Vehicle receivables						7.1						7.1						—						7.8						7.8						—
Total other asset-backed securities						18.3						18.3						—						19.1						19.1						—
Total mortgage and asset-backed securities						250.1						250.1						—						218.5						218.5						—
Collateralized loan obligations						127.6						127.6						—						—						—						—
Total mortgage and asset-backed securities and collateralized loan obligations						$	377.7					$	377.7					$	—					$	218.5					$	218.5					$	—

(1)    Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. Government (i.e., GNMA) or are guaranteed

by a government sponsored entity (i.e., FNMA, FHLMC).

Schedule of carrying values for other long-term investments

The following table presents the carrying values of White Mountains’s other long-term investments as of September 30, 2021 and December 31, 2020:

						Fair Value at
Millions						September 30, 2021						December 31, 2020
Kudu’s Participation Contracts						$	604.7					$	400.6
PassportCard/DavidShield						105.0						95.0
Elementum Holdings L.P.						56.7						55.1
Other unconsolidated entities (1)						27.0						42.4
Total unconsolidated entities						793.4						593.1
Private equity funds and hedge funds						144.2						121.2
Bank loan fund						161.7						—
Lloyd’s trust deposits						111.2						—
ILS funds						53.9						51.4
Private debt investments						13.3						21.1
Other						7.8						—
Total other long-term investments						$	1,285.5					$	786.8

(1) Includes White Mountains’s non-controlling equity interests in certain private common equity securities, limited liability companies and convertible preferred securities and Simple Agreement for Future Equity (“SAFE”) investments.

Other long-term investments

The following table presents the fair value of investments and unfunded commitments in private equity funds and hedge funds by investment objective and sector as of September 30, 2021 and December 31, 2020:

						September 30, 2021												December 31, 2020
Millions						Fair Value						Unfunded Commitments						Fair Value						Unfunded Commitments
Private equity funds
Aerospace/Defense/Government						$	63.9					$	14.0					$	69.1					$	15.3
Financial services						63.2						29.6						23.5						30.4
Real estate						4.8						2.9						—						—
Manufacturing/Industrial						.1						—						28.6						—
Total private equity funds						132.0						46.5						121.2						45.7
Hedge funds
European small/mid cap						12.2						—						—						—
Total hedge funds						12.2						—						—						—
Total private equity funds and hedge funds    included in other long-term investments						$	144.2					$	46.5					$	121.2					$	45.7

Fair value of private equity funds subject to lock-up periods

The following table presents investments in private equity funds that were subject to lock-up periods as of September 30, 2021:

Millions						1 – 3 years						3 – 5 years						5 – 10 years						>10 years						Total
Private equity funds — expected lock-up period remaining						$.3						$14.0						$109.0						$8.7						$132.0

Rollforward of fair value investments by level

The following tables present the changes in White Mountains’s fair value measurements by level for the nine months ended September 30, 2021 and 2020:

															Level 3  Investments			Other Long-term Investments Measured at NAV (1)
Millions			Level 1 Investments			Level 2  Investments									Other Long-term Investments									Total
Balance at December 31, 2020			$	978.5		$	1,030.9								$	614.2		$	172.6					$	2,796.2		(2)
Net realized and unrealized gains (losses)			(327.6)			(13.1)									79.0			33.9						(227.8)			(3)
Amortization/Accretion			(.1)			(5.9)									—			—						(6.0)
Purchases			130.9			989.7									143.6			199.6						1,463.8
Sales			(257.7)			(284.9)									(31.9)			(70.9)						(645.4)
Effect of Ark Transaction			—			68.2									9.6			135.8						213.6
Transfers in			—			—									—			—						—
Transfers out			—			—									—			—						—
Balance at September 30, 2021			$	524.0		$	1,784.9								$	814.5		$	471.0					$	3,594.4		(2)

(1) Consists of private equity funds, a hedge fund, Lloyd’s trust deposits, a bank loan fund, and ILS funds for which fair value is measured at NAV using the practical expedient. Investments for which fair value is measured at NAV are not classified within the fair value hierarchy. See Note 1 — “Basis of Presentation and Significant Accounting Policies”.

(2) Excludes carrying value of $609.5 and $142.9 as of September 30, 2021 and December 31, 2020 classified as short-term investments.

(3) Includes amounts attributable to TPC Providers of $6.5 for the nine months ended September 30, 2021.

																		Level 3  Investments			Other Long-term Investments Measured at NAV (1)
Millions			Level 1 Investments			Level 2  Investments						Common Equity Securities						Other Long-term Investments and Investment in MediaAlpha Pre-IPO						Total
Balance at December 31, 2019			$	780.0		$	1,109.6					$	.1					$	654.0		$	202.3		$	2,746.0		(2)
Net realized and unrealized gains (losses)			29.2			12.5						—						275.6			(14.9)			302.4			(3)
Amortization/Accretion			—			(3.0)						—						—			—			(3.0)
Purchases			128.8			316.2						—						78.8			39.8			563.6
Sales			(642.7)			(368.5)						—						(8.1)			(56.3)			(1,075.6)
Transfers in			—			—						—						—			—			—
Transfers out			—			—						—						—			—			—
Balance at September 30, 2020			$	295.3		$	1,066.8					$	.1					$	1,000.3		$	170.9		$	2,533.4		(2)

(1) Includes private equity funds, a hedge fund and ILS funds for which fair value is measured at NAV using the practical expedient are no longer classified within the fair value hierarchy. See Note 1 — “Basis of Presentation and Significant Accounting Policies”.

(2) Excludes carrying value of $571.8 and $201.2 as of September 30, 2020 and December 31, 2019 classified as short-term investments.

(3) Excludes realized and unrealized gains associated with short-term investments of $0.4 for the nine months ended September 30, 2020.

Schedule of significant unobservable inputs used in estimating the fair value of investment securities

The following tables present significant unobservable inputs used in estimating the fair value of White Mountains’s other long-term investments, classified within Level 3 as of September 30, 2021 and December 31, 2020. The tables below exclude $14.9 million and $27.6 million of Level 3 other long-term investments generally valued based on recent or expected transaction prices. The fair value of investments in private equity funds, hedge funds, Lloyd’s trust deposits, bank loans funds and ILS funds are generally estimated using the NAV of the funds.

$ in Millions

September 30, 2021

Description

Valuation Technique(s) (1)

Fair Value (2)

Unobservable Inputs

Discount Rate (3)(4)

Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (4)

Kudu’s Participation Contracts (5)(6)

Discounted cash flow

$604.7

18% - 23%

7x - 13x

PassportCard/DavidShield

Discounted cash flow

$105.0

23%

4%

Elementum Holdings, L.P.

Discounted cash flow

$56.7

17%

4%

Private debt investments

Discounted cash flow

$11.2

4% - 8%

N/A

Other

Discounted cash flow

$22.0

20% - 24%

4%

(1) Key inputs to the discounted cash flow analysis generally include projections of future revenue and earnings, discount rates and terminal exit multiples or growth rates.

(2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs.

(3) Since Kudu’s Participation Contracts are not subject to corporate taxes within Kudu Investment Management, LLC, pre-tax discount rates are applied to pre-tax cash flows in determining fair values.

(4) Increases (decreases) to the discount rates in isolation would result in lower (higher) fair value measurements, while increases (decreases) to the terminal cash flow exit multiples or terminal revenue growth rates in isolation would result in higher (lower) fair value measurements.

(5) For the nine months ended September 30, 2021, Kudu deployed a total of $141.6 in new and existing Kudu Participation Contracts, including TIG Advisors, TK Partners, Third Eye Capital Management and Douglass Winthrop Advisors.

(6) As of September 30, 2021, certain Kudu Participation Contracts with a total fair value of $121.0 were valued using a probability weighted expected return method, which was based on a discounted cash flow analysis and an expected sale transaction.

$ in Millions

December 31, 2020

Description

Valuation Technique(s) (1)

Fair Value (2)

Unobservable Inputs

Discount Rate (3)(4)

Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (4)

Kudu’s Participation Contracts (5)

Discounted cash flow

$400.6

18% - 23%

7x - 12x

PassportCard/DavidShield (6)

Discounted cash flow

$95.0

23%

4%

Elementum Holdings, L.P.

Discounted cash flow

$55.1

17%

4%

Private debt investments

Discounted cash flow

$17.1

4% - 8%

N/A

Other

Discounted cash flow

$18.8

20% - 24%

4%

(1) Key inputs to the discounted cash flow analysis generally include projections of future revenue and earnings, discount rates and terminal exit multiples or growth rates.

(2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs.

(3) Since Kudu’s Participation Contracts are not subject to corporate taxes within Kudu Investment Management, LLC, pre-tax discount rates are applied to pre-tax cash flows in determining fair values.

(4) Increases (decreases) to the discount rates in isolation would result in lower (higher) fair value measurements, while increases (decreases) to the terminal cash flow exit multiples or terminal revenue growth rates in isolation would result in higher (lower) fair value measurements.

(5) In 2020, Kudu deployed a total of $118.2 in new Kudu Participation Contracts, including Creation Investments Capital, Sequoia Financial Group, Channel Capital and Ranger Investment Management.

(6) In 2020, White Mountains made an additional $15.0 investment in PassportCard/DavidShield. See Note 2 — “Significant Transactions”.

X

- Definition

Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of the amount of gains or losses for the period included in earnings or resulted in a change to net assets, have arisen from the use of significant unobservable inputs (level 3) to measure the fair value of assets, liabilities, and financial instruments classified in shareholders' equity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarningsTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of information about investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5B
-URI http://asc.fasb.org/extlink&oid=121645371&loc=SL120269825-111563

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5A
-URI http://asc.fasb.org/extlink&oid=121645371&loc=SL120269820-111563

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of investment income, including, but not limited to, interest and dividend income and amortization of discount (premium) derived from debt and equity securities. Excludes realized and unrealized gain (loss) on investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(a),(b))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

+ Details

Name:	us-gaap_InvestmentIncomeTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- Definition

Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of other investments not readily marketable, including, but not limited to, description of investment, fair value and value as measured by quoted price.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 820
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35710923&loc=d3e45360-110995

+ Details

Name:	us-gaap_ScheduleOfOtherInvestmentsNotReadilyMarketableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

No definition available.

+ Details

Name:	us-gaap_TradingSecuritiesAndCertainTradingAssetsTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of the fair value measurement of assets measured at fair value on a recurring basis, including a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: total gains or losses for the period (realized and unrealized), amortization or accretion of discount, purchases, sales, issuances, transfers in and transfers out of each level of the fair value hierarchy by class of asset.

+ References

No definition available.

+ Details

Name:	wtm_FairValueAssetsMeasuredOnRecurringBasisMeasurementInputReconciliationTableTextBlock
Namespace Prefix:	wtm_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of hedge funds and private equity investments held at fair value by investment objective or sector and the amount of unfunded commitments associated with each objective or sector.

+ References

No definition available.

+ Details

Name:	wtm_HedgeFundAndPrivateEquityInvestmentByObjectiveOrSectorTableTextBlock
Namespace Prefix:	wtm_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of fixed maturity securities by credit quality indicator.

+ References

No definition available.

+ Details

Name:	wtm_InvestmentFixedMaturitySecuritiesCreditQualityIndicatorsTableTextBlock
Namespace Prefix:	wtm_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of expected lock up period of private equity investments.

+ References

No definition available.

+ Details

Name:	wtm_PrivateEquityLockUpPeriodTableTextBlock
Namespace Prefix:	wtm_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of realized and unrealized gains and losses on investments reported in the statement of income.

+ References

No definition available.

+ Details

Name:	wtm_ScheduleOfRealizedAndUnrealizedGainLossOnInvestmentsTableTextBlock
Namespace Prefix:	wtm_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration