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v3.20.1

Leases - Additional Information (Details) | Mar. 31, 2020 USD ($)
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Leases [Abstract] |
Additional operating lease not yet commenced | $ 0

X
- Definition Lessee, Operating Lease, Lease Not Yet Commenced, Amount + References No definition available. + Details
Name: | alg_LesseeOperatingLeaseLeaseNotYetCommencedAmount
Namespace Prefix: | alg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration