Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Fair value measurements
Cash and cash equivalents	$ 139,067	$ 138,960	$ 77,670
Fair value measured on a recurring basis
Fair value measurements
Cash and cash equivalents	139,067	138,960	77,670
Available for sale securities	162,080	177,292	199,944
Trading securities	68,717	76,183	69,260
Total assets measured at fair value	369,291	392,570	346,526
Fair value measured on a recurring basis \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	(93)	14	(197)
Fair value measured on a recurring basis \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(480)	121	(151)
Fair value measured on a recurring basis \| Level 1
Fair value measurements
Cash and cash equivalents	139,067	138,960	77,670
Available for sale securities	3,441	3,588	3,041
Trading securities	41,692	48,260	42,866
Total assets measured at fair value	183,720	190,929	123,426
Fair value measured on a recurring basis \| Level 1 \| Commodity futures contracts
Fair value measurements
Derivative instruments, net	(480)	121	(151)
Fair value measured on a recurring basis \| Level 2
Fair value measurements
Available for sale securities	158,639	173,704	196,903
Trading securities	27,025	27,923	26,394
Total assets measured at fair value	185,571	201,641	223,100
Fair value measured on a recurring basis \| Level 2 \| Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	$ (93)	$ 14	$ (197)

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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