Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Fair value measurements
Cash and cash equivalents	$ 106,289	$ 138,960	$ 57,857
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	106,289	138,960	57,857
Available for sale securities	187,868	177,292	206,687
Trading securities	78,285	76,183	71,375
Total assets measured at fair value	372,776	392,570	335,790
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	428	14	(17)
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(94)	121	(112)
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	106,289	138,960	57,857
Available for sale securities	3,169	3,588	3,078
Trading securities	50,664	48,260	45,110
Total assets measured at fair value	160,028	190,929	105,933
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(94)	121	(112)
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	184,699	173,704	203,609
Trading securities	27,621	27,923	26,265
Total assets measured at fair value	212,748	201,641	229,857
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ 428	$ 14	$ (17)

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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