Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 91,547	$ 86,198	$ 76,037
Other Comprehensive Income (Loss):
Foreign currency translation adjustments (Note 19)	26,293	(8,533)	(45,490)
Defined benefit pension plans:
Net actuarial gain (loss) arising in period (net of taxes of $771, $3,391, and $568 for 2017, 2016 and 2015, respectively)	(582)	3,818	1,311
Amortization of prior service cost included in pension expense (net of taxes of $4, $4, and $6 for 2017, 2016 and 2015, respectively)	10	10	11
Amortization of actuarial loss included in pension expense (net of taxes of $1,240, $1,301, and $1,755 for 2017, 2016 and 2015, respectively)	2,269	2,207	3,002
Net defined benefit pension plan activity (Note 19)	1,697	6,035	4,324
Cash flow hedges:
Losses arising in period (net of taxes of $0, $9 , and $26 in 2017, 2016 and 2015, respectively)		(19)	(49)
Reclassifications to income in period (net of taxes of $0, $28, and $8 in 2017, 2016 and 2015, respectively)	(9)	45	5
Net cash flow hedge activity (Note 19)	(9)	26	(44)
Other Comprehensive Income (Loss)	27,981	(2,472)	(41,210)
Comprehensive Income	119,528	83,726	34,827
Comprehensive (Income) Loss Attributable to Noncontrolling Interests	(48)	88	(2)
Comprehensive Income Attributable to Stepan Company	$ 119,480	$ 83,814	$ 34,825