Fair Value Measurements Fair Value Measurements Narratives (Details)	3 Months Ended
Mar. 31, 2020 USD ($)
Fair Value Disclosures [Abstract]
Transfers between levels, fair value disclosure	$ 0

Amount of transfers of assets measured on a recurring basis between Levels of the fair value hierarchy.

No definition available.

Name:	wtba_TransfersBetweenLevelsFairValueDisclosure
Namespace Prefix:	wtba_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration