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

Lessee, Operating Lease, Lease Not Yet Commenced, Amount

No definition available.

Name:	alg_LesseeOperatingLeaseLeaseNotYetCommencedAmount
Namespace Prefix:	alg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant