Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Out-of-period adjustments	$ 5,100
Equity in net income of unconsolidated investments	84,487	$ 59,637	$ 27,978
Joint ventures	499,756	429,794
Foreign exchange transaction (losses) gains	$ (11,100)	$ 2,400	$ 51,800
Maximum remaining expiration period for foreign currency forward contracts	1 year
Excess tax benefits	$ 8,800
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	2 years
Definite-lived intangible assets useful life	5 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	60 years
Definite-lived intangible assets useful life	25 years
Planned Major Maintenance Activities
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	12 months
Saudi Organometallic Chemicals Company
Summary Of Significant Accounting Policies [Line Items]
Ownership percentage	50.00%
Equity in net income of unconsolidated investments	$ 3,800
Joint ventures	$ 4,500