Summary of Significant Accounting Policies - Environmental Matters and Turnaround Expenses (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Environmental Matters
Liabilities recognized for environmental remediation matters	$ 0	$ 0
Nitrogen Fertilizer Segment
Planned Major Maintenance Activities [Line Items]
Turnaround costs	$ 9,800,000	$ 6,400,000	$ 2,600,000
Minimum
Planned Major Maintenance Activities [Line Items]
Frequency of planned major maintenance activities	2 years
Maximum
Planned Major Maintenance Activities [Line Items]
Frequency of planned major maintenance activities	3 years