Number of installment payments of employee related payables.

No definition available.

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- Definition

The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

No definition available.

+ Details

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

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

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- 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

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_TitleOfIndividualAxis=agr_OfficersAndEmployeesMember
Namespace Prefix:
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Balance Type:
Period Type:

Stock-Based Compensation Expense (Detail) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Jun. 30, 2018 $ / shares shares	Mar. 31, 2019 USD ($) Installment	Mar. 31, 2018 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $		$ 0.8	$ (0.1)
Performance Shares Units \| Officers and Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares) \| shares	1,358
Number of installment payments of employee related payables \| Installment		3
Share-based payment award options grant date fair value (in usd per share) \| $ / shares	$ 31.80