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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Income
Net income available to IFF common shareholders	$ 337,302	$ 295,665	$ 405,031
Less: Increase in redemption value of redeemable noncontrolling interests in excess of earnings allocated	(2,848)	0	0
Net income available to IFF common shareholders	$ 334,454	$ 295,665	$ 405,031
Shares
Average number of shares outstanding - basic (in shares)	87,551	79,070	79,648
Average number of shares outstanding - diluted (in shares)	88,121	79,370	79,981
Net Income per Share
Net income per share - basic (in dollars per share)	$ 3.81	$ 3.73	$ 5.07
Net income per share - diluted (in dollars per share)	$ 3.79	$ 3.72	$ 5.05
Employee Stock Option And Restricted Stock [Member]
Shares
Adjustment for assumed dilution (in shares)	303	300	333
SPC [Member]
Shares
Adjustment for assumed dilution (in shares)	267	0	0