Net Sales - Summary of Net Sales Disaggregated by Principal Markets (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net sales:
Net sales	$ 88,903	$ 73,969	$ 105,033	$ 83,411	$ 73,896	$ 75,495	$ 121,527	$ 94,152	$ 351,316	$ 365,070	$ 378,160
Chemical [Member]
Net sales:
Net sales									351,316	365,070	378,160
Chemical [Member] | Agricultural Products [Member]
Net sales:
Net sales									180,036	187,641	187,164
Chemical [Member] | Industrial Products
Net sales:
Net sales									133,024	139,643	148,598
Chemical [Member] | Mining Products [Member]
Net sales:
Net sales									$ 38,256	$ 37,786	$ 42,398