Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Fair value measurements
Cash and cash equivalents	$ 96,617	$ 166,841	$ 106,289
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	96,617	166,841	106,289
Available for sale securities	223,410	188,282	187,868
Trading securities	83,867	73,828	78,285
Total assets measured at fair value	405,365	430,670	372,776
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	717	778	428
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	754	941	(94)
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	96,617	166,841	106,289
Available for sale securities	2,616	3,149	3,169
Trading securities	70,879	61,431	50,664
Total assets measured at fair value	170,866	232,362	160,028
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	754	941	(94)
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	220,794	185,133	184,699
Trading securities	12,988	12,397	27,621
Total assets measured at fair value	234,499	198,308	212,748
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ 717	$ 778	$ 428

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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