Fair Value Measurements - Transfers (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Fair Value Measurements
Amount of transfers of assets and liabilities measured on a recurring basis between Levels 1, 2 and 3 of the fair value hierarchy	$ 0	$ 0

Amount of transfers of assets and liabilities measured on a recurring basis between Levels 1, 2 and 3 of the fair value hierarchy.

No definition available.

Name:	gkos_FairValueAssetsAndLiabilitiesLevel1Level2AndLevel3TransfersAmount
Namespace Prefix:	gkos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant