Acquisitions - Additional Information (Detail)				3 Months Ended										12 Months Ended
		Mar. 26, 2018 USD ($) ft² T	Oct. 03, 2016 USD ($) Customer T	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 BRL (R$)	Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)	Mar. 31, 2017 BRL (R$)	Dec. 31, 2016 BRL (R$)	Oct. 03, 2016 BRL (R$) Customer T
Business Acquisition [Line Items]
Paid from cash on hand														$ 22,852,000		$ 4,339,000		$ 23,510,000
Goodwill				$ 22,954,000				$ 25,118,000				$ 25,308,000		22,954,000		25,118,000		25,308,000
Net sales				466,659,000	$ 507,997,000	$ 519,866,000	$ 499,335,000	473,823,000	$ 487,814,000	$ 495,101,000	$ 468,269,000			1,993,857,000	[1]	1,925,007,000	[1]	1,766,166,000	[1]
Net income				26,946,000	$ 22,168,000	$ 32,925,000	$ 30,723,000	9,884,000	$ 21,899,000	$ 27,882,000	31,913,000			$ 112,762,000		91,578,000		86,191,000
Non-compete Agreements [Member]
Business Acquisition [Line Items]
Amortization periods for the identifiable intangible assets at the time of acquisition														5 years
Minimum [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Amortization periods for the identifiable intangible assets at the time of acquisition														10 years
Maximum [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Amortization periods for the identifiable intangible assets at the time of acquisition														13 years
Brazil [Member]
Business Acquisition [Line Items]
Net sales	[1]													$ 100,328,000		109,960,000		74,961,000
Surfactants [Member]
Business Acquisition [Line Items]
Goodwill				17,054,000				$ 19,160,000				19,491,000		17,054,000		19,160,000		19,491,000
Net sales														1,385,932,000		$ 1,297,555,000		1,181,563,000
2018 Acquisition [Member] | BASF Mexicana, S.A. DE C.V. [Member]
Business Acquisition [Line Items]
Total assets acquired		$ 22,852,000
2018 Acquisition [Member] | BASF Mexicana, S.A. DE C.V. [Member] | Surfactants [Member] | Ecatepec, Mexico [Member]
Business Acquisition [Line Items]
Incremental inventory and related value-added taxes				1,377,000										1,377,000
Capacity of production facility expected to be acquired | T		50,000
Warehouse space, laboratory and office space currently expected to be acquired | ft²		124,000
Paid from cash on hand		$ 21,475,000
Total assets acquired				22,852,000										22,852,000
Payment of incremental inventory and related value-added taxes				1,377,000
Intangible assets identified related to acquisition				$ 0										$ 0
2016 Acquisition [Member] | Tebras And PBC [Member]
Business Acquisition [Line Items]
Total assets acquired			$ 32,442,000
Goodwill			14,207,000
Acquisition of intangible assets			7,354,000
2016 Acquisition [Member] | Tebras And PBC [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Acquisition of intangible assets			$ 4,331,000
Amortization periods for the identifiable intangible assets at the time of acquisition			13 years
2016 Acquisition [Member] | Tebras And PBC [Member] | Supply Contract [Member]
Business Acquisition [Line Items]
Acquisition of intangible assets			$ 2,555,000
Amortization periods for the identifiable intangible assets at the time of acquisition			4 years
2016 Acquisition [Member] | Tebras And PBC [Member] | Non-compete Agreements [Member]
Business Acquisition [Line Items]
Acquisition of intangible assets			$ 468,000
Amortization periods for the identifiable intangible assets at the time of acquisition			5 years
2016 Acquisition [Member] | Tebras And PBC [Member] | Before purchase accounting adjustments [Member]
Business Acquisition [Line Items]
Goodwill											14,327,000
2016 Acquisition [Member] | Tebras And PBC [Member] | After purchase accounting adjustments [Member]
Business Acquisition [Line Items]
Goodwill											14,207,000
2016 Acquisition [Member] | Tebras And PBC [Member] | Brazil [Member]
Business Acquisition [Line Items]
Net sales																				$ 28,000,000
2016 Acquisition [Member] | Tebras And PBC [Member] | Brazil [Member] | Maximum [Member]
Business Acquisition [Line Items]
Net income																				$ 2,000,000
2016 Acquisition [Member] | Tebras And PBC [Member] | Surfactants [Member] | Brazil [Member]
Business Acquisition [Line Items]
Capacity of production facility expected to be acquired | T			25,000																				25,000
Paid from cash on hand												21,812,000	R$ 70,000,000
Original purchase price of acquisitions			$ 29,075,000																				R$ 93,309,000
Deposited in escrow												2,804,000						2,804,000				R$ 9,000,000
Unpaid working capital adjustments												$ 4,459,000						$ 4,459,000				R$ 14,309,000
Working capital adjustment amount paid											4,339,000										R$ 13,925,000
Adjusted purchase price of the acquisitions											$ 28,955,000										R$ 92,925,000
2016 Acquisition [Member] | Tebras And PBC [Member] | Surfactants [Member] | Brazil [Member] | Minimum [Member]
Business Acquisition [Line Items]
Number of customers | Customer			1,200																				1,200

[1] Net sales are attributed to countries based on the location of the Company facility making the sales.