Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Facility Customer Derivative Segment	Dec. 31, 2017 USD ($) Derivative	Dec. 31, 2016 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of facilities for manufacture and distribution of products | Facility	4
Number of customers accounted as percentage of accounts receivable | Customer	6
Percentage of net receivables	39.00%
Inventory reserves	$ 278,000	$ 933,000
Long-lived assets, held for sale	0	0
Impairments of goodwill			$ 1,621,000
Interest cost capitalized	0	300,000	$ 15,000,000
Insurance coverage of general liability and auto liability risks	100,000,000
Insurance policy covering pollution liability	$ 50,000,000
Tax benefit recognized	Greater than 50%
Incentive tax credit receivable		$ 8,100,000
Number of derivatives held with fair value eligible for offset | Derivative	0	0
Number of reportable segment | Segment	1
Increase operating lease, right-of-use asset	$ 15,000,000
Increase operating lease, obligation liability	15,000,000
Cost of Sales [Member]
Summary Of Significant Accounting Policies [Line Items]
Incentive tax credit receivable		$ 700,000
Plant, Property and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Incentive tax credit receivable	$ 3,100,000	$ 7,400,000
Customer [Member] | Net Sales [Member] | Covestro [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of total net sales		12.00%	13.00%
Customer [Member] | Net Sales [Member] | Coffeyville Resources Nitrogen Fertilizers L.L.C. [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of total net sales	11.00%
Customer [Member] | Net Sales [Member] | Koch Fertilizer LLC [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of total net sales	13.00%	10.00%	11.00%