Income Taxes (Details) $ in Millions	3 Months Ended
Sep. 30, 2018 USD ($)
Income Tax Disclosure [Abstract]
Federal tax expense decrease, deemed repatriation	$ 4.2
Federal tax expense increase, impact of rate change on deferred	$ 1.2

Amount of reasonable estimate for income tax expense from transition tax on accumulated earnings of controlled foreign corporation deemed repatriated pursuant to Tax Cuts and Jobs Act for which accounting for tax effect is incomplete.

No definition available.

Name:	alg_TaxCutsAndJobsActOf2017IncompleteAccountingTransitionTaxForAccumulatedForeignEarningsProvisionalIncomeTaxExpense
Namespace Prefix:	alg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration