Net Income Per Share - Reconciliation of Shares Used in Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
	Sep. 17, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to IFF stockholders		$ 84,828	$ 127,124	$ 295,639	$ 372,330
Adjustment related to decrease in redemption value of redeemable noncontrolling interests in excess of earnings allocated		864	1,736	4,964	1,593
Net income available to IFF stockholders		$ 85,692	$ 128,860	$ 300,603	$ 373,923
Weighted average common shares outstanding (basic) (in shares)		112,183	111,998	112,148	111,953
Weighted average shares assuming dilution (diluted) (in shares)		113,622	113,493	113,631	113,133
Net income per share - basic (in dollars per share)		$ 0.76	$ 1.15	$ 2.68	$ 3.34
Net income per share - diluted (in dollars per share)		$ 0.75	$ 1.13	2.64	3.30
Tangible Equity Units, Price for Shares Diluted	$ 0.3839			$ 0.3839	$ 0.3839
Stock options and restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Adjustment for assumed dilution (in shares)		276	332	320	372
SPC portion of TEUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Adjustment for assumed dilution (in shares)		1,163	1,163	1,163	808