Consolidated Statements of Equity (unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018
Statement of Stockholders' Equity [Abstract]
Share repurchases (in shares)	5,200	56	130,900		45,000
Share repurchases	$ 0.1		$ 3.3	[1]	$ 1.3	[1]
Cash payments for tax withholding obligations			$ 3.3		$ 1.3

[1] During the nine months ended September 30, 2019 and 2018, GCP withheld and retained approximately 131,000 shares and 45,000 shares, respectively, of Company common stock in a non-cash transaction with a cost of $3.3 million and $1.3 million, respectively, in connection with fulfilling statutory tax withholding requirements for employees under the provisions of the Company's equity compensation programs. During the nine months ended September 30, 2019 and 2018, cash payments for such tax withholding obligations were $3.3 million and $1.3 million, respectively.