Investment Securities - Proceeds from the call of held-to-maturity investment securities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investment Securities
Proceeds	$ 101	$ 348	$ 827	$ 1,763
Realized gains		$ 11		$ 11

Amount of gain on sale of investment in debt security measured at amortized cost (held-to-maturity), including other-than-temporary impairment (OTTI).

No definition available.

Name:	alrs_DebtSecuritiesHeldToMaturitySoldRealizedGain
Namespace Prefix:	alrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration