Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Fair value measurements
Cash and cash equivalents	$ 136,291	$ 166,841	$ 139,067
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	136,291	166,841	139,067
Available for sale securities	207,874	188,282	162,080
Trading securities	78,271	73,828	68,717
Total assets measured at fair value	423,861	430,670	369,291
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	755	778	(93)
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	670	941	(480)
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	136,291	166,841	139,067
Available for sale securities	3,144	3,149	3,441
Trading securities	65,532	61,431	41,692
Total assets measured at fair value	205,637	232,362	183,720
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	670	941	(480)
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	204,730	185,133	158,639
Trading securities	12,739	12,397	27,025
Total assets measured at fair value	218,224	198,308	185,571
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ 755	$ 778	$ (93)

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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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