Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Fair value measurements
Cash and cash equivalents	$ 76,210	$ 166,841	$ 108,264
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	76,210	166,841	108,264
Available for sale securities	235,912	188,282	193,843
Trading securities	83,905	73,828	66,120
Total assets measured at fair value	396,883	430,670	369,181
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	504	778	539
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	352	941	415
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	76,210	166,841	108,264
Available for sale securities	2,313	3,149	3,173
Trading securities	70,762	61,431	53,504
Total assets measured at fair value	149,637	232,362	165,356
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	352	941	415
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	233,599	185,133	190,670
Trading securities	13,143	12,397	12,616
Total assets measured at fair value	247,246	198,308	203,825
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ 504	$ 778	$ 539

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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