Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Fair value measurements
Cash and cash equivalents	$ 87,400	$ 110,899	$ 64,333
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	87,400	110,899	64,333
Available for sale securities	183,784	183,289	189,172
Trading securities	71,790	62,260	67,594
Total assets measured at fair value	342,744	355,454	320,417
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	(122)	(407)	177
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(108)	(587)	(859)
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	87,400	110,899	64,333
Available for sale securities	3,584	3,000	732
Trading securities	71,790	62,260	67,594
Total assets measured at fair value	162,666	175,572	131,800
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(108)	(587)	(859)
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	180,200	180,289	188,440
Total assets measured at fair value	180,078	179,882	188,617
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ (122)	$ (407)	$ 177

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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