Fair Value Measurements Fair Value Measurements (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($)
Fair Value Disclosures [Abstract]
Restructuring reserve, period increase (decrease), related to impairments of operating lease right-of-use assets	$ 1.3

Amount of increase (decrease) in the accrual for restructuring costs related to impairments of operating lease right-of-use assets.

No definition available.

Name:	blkb_RestructuringReservePeriodIncreaseDecreaseRelatedtoImpairmentofOperatingLeaseRightofUseAssets
Namespace Prefix:	blkb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration