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. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to IFF stockholders	$ 127,124	$ 95,716	$ 372,330	$ 324,281
Add: Reduction in redemption value of redeemable noncontrolling interests in excess of earnings allocated	1,736	0	1,593	0
Net income available to IFF stockholders	$ 128,860	$ 95,716	$ 373,923	$ 324,281
Weighted average common shares outstanding (basic) (in shares)	111,998	81,263	111,953	79,783
Weighted average shares assuming dilution (diluted) (in shares)	113,493	81,647	113,133	80,115
Net income per share - basic (in dollars per share)	$ 1.15	$ 1.18	$ 3.34	$ 4.06
Net income per share - diluted (in dollars per share)	$ 1.13	$ 1.17	$ 3.30	$ 4.04
Stock options and restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Adjustment for assumed dilution (in shares)	332	267	372	293
SPC portion of TEUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Adjustment for assumed dilution (in shares)	1,163	117	808	39