Common stock dividend rate percentage.

No definition available.

Name:	argo_CommonStockDividendRatePercentage
Namespace Prefix:	argo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Count of other than stock option shares settle in common shares.

+ References

No definition available.

+ Details

Name:	argo_CountOfOtherThanStockOptionSharesSettleInCommonShares
Namespace Prefix:	argo_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment awards, decrease in exercise due to stock dividend.

+ References

No definition available.

+ Details

Name:	argo_ShareBasedCompensationArrangementByShareBasedPaymentAwardsDecreaseInExerciseDueToStockDividend
Namespace Prefix:	argo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment awards, percentage increase in awards outstanding due to stock dividend.

+ References

No definition available.

+ Details

Name:	argo_ShareBasedCompensationArrangementByShareBasedPaymentAwardsPercentageIncreaseInAwardsOutstandingDueToStockDividend
Namespace Prefix:	argo_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

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

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=argo_StockSettledSARsActivityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=argo_CashSettledSARsActivityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=argo_TwoThousandSevenPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=argo_TwoThousandFourteenPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=argo_ShareOptionsandStockAppreciationRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=argo_RestrictedSharesRSUsPerformanceUnitsPerformanceSharesandOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Share-based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2014	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Nov. 30, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years				5 years	5 years
Stock divided declared		15.00%		15.00%
Percentage increase in number of awards outstanding due to stock dividend				15.00%
Reduction in exercise price of awards outstanding due to stock dividend				13.04%
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period				7 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, compensation expense		$ 4,800,000	$ 2,400,000	$ 8,200,000	$ 5,200,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		26,600,000		$ 26,600,000
Restricted Stock Units (RSUs) [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years				1 year
Restricted Stock Units (RSUs) [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years				8 years
Stock-Settled SARs Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, compensation expense		400,000	2,000,000	$ 1,500,000	2,700,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		1,200,000		$ 1,200,000
Stock-Settled SARs Activity [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years				1 year
Stock-Settled SARs Activity [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years				4 years
Cash Settled S A Rs Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, compensation expense		300,000	$ 2,300,000	$ 800,000	$ 900,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		$ 0		$ 0
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)						4,500,000.0
Share-based compensation arrangement by share-based payment award, number of shares available for grant (in shares)	1,460,000.00
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, additional number of shares authorized (in shares)	2,800,000.0
2007 Plan [Member] \| Share Options and Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Count of restricted shares, settle in common shares (in shares)				1
2007 Plan [Member] \| Restricted Shares, RSUs, Performance Units, Performance Shares, and Other [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Count of restricted shares, settle in common shares (in shares)				2.75