Investment Securities - Proceeds from the call of held-to-maturity investment securities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Investment Securities
Proceeds	$ 116	$ 101	$ 242	$ 827

The cash inflow associated with the sale or calls of securities that had been designated as held-to-maturity.

No definition available.

Name:	alrs_ProceedsFromSaleOrCallsOfHeldToMaturitySecurities
Namespace Prefix:	alrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration