Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Fair value measurements
Cash and cash equivalents	$ 108,264	$ 138,960	$ 87,400
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	108,264	138,960	87,400
Available for sale securities	193,843	177,292	183,784
Trading securities	66,120	76,183	71,790
Total assets measured at fair value	369,181	392,570	342,744
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	539	14	(122)
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	415	121	(108)
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	108,264	138,960	87,400
Available for sale securities	3,173	3,588	3,584
Trading securities	53,504	48,260	44,975
Total assets measured at fair value	165,356	190,929	135,851
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	415	121	(108)
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	190,670	173,704	180,200
Trading securities	12,616	27,923	26,815
Total assets measured at fair value	203,825	201,641	206,893
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ 539	$ 14	$ (122)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Fair value of asset after deduction of liability.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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