Earnings Per Share - Narrative (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Treasury stock purchased	$ 0.7	$ 0.9	[1]
2016 Stock Incentive Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Share repurchases (in shares)	23	33
Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	600	700
Stock Option | Continuing operations
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,600	2,000
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	300	400
Restricted Stock Units (RSUs) | Continuing operations
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	400	500

[1] For the quarter ending March 31, 2017, GCP repurchased approximately 33,000 shares of Company common stock for $0.9 million in connection with its equity compensation programs; number of shares is not included in the table above due to rounding.