Note 9 - Estimated Liability for Appeals (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Estimated Liability for Appeals Gain (Loss) Included in Earnings	$ 8,400	$ 8,436

The amount of gain (loss) realized by the release of estimated liability for appeals during the period.

No definition available.

Name:	hmsy_EstimatedLiabilityForAppealsGainLossIncludedInEarnings
Namespace Prefix:	hmsy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration