Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Fair value measurements
Cash and cash equivalents	$ 64,333	$ 96,314	$ 49,512
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	64,333	96,314	49,512
Available for sale securities	189,172	171,596	193,169
Trading securities	67,594	60,520	75,094
Total assets measured at fair value	320,417	328,541	317,558
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	177	79	147
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(859)	32	(364)
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	64,333	96,314	49,512
Available for sale securities	732	1,200	2,402
Trading securities	67,594	60,520	75,094
Total assets measured at fair value	131,800	158,066	126,644
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(859)	32	(364)
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	188,440	170,396	190,767
Total assets measured at fair value	188,617	170,475	190,914
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ 177	$ 79	$ 147

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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-Publisher FASB
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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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