FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2017

FAIR VALUE MEASUREMENTS

Schedule of financial assets and liabilities measured at fair value

	Estimated Fair Value December 31, 2017
	Total		Input Levels Used
	Fair Value		Level 1		Level 2		Level 3
Cash and equivalents	$	96,314	$	96,314	$	—	$	—
Available for sale securities		171,596		1,200		170,396		—
Foreign currency forward contracts		79		—		79		—
Commodity futures contracts, net		32		32		—		—
Trading securities		60,520		60,520		—		—
Total assets measured at fair value	$	328,541	$	158,066	$	170,475	$	—

	Estimated Fair Value December 31, 2016
	Total		Input Levels Used
	Fair Value		Level 1		Level 2		Level 3
Cash and equivalents	$	119,145	$	119,145	$	—	$	—
Available for sale securities		164,183		2,419		161,764		—
Foreign currency forward contracts		(119)		—		(119)		—
Commodity futures contracts, net		1,746		1,746		—		—
Trading securities		67,995		67,995		—		—
Total assets measured at fair value	$	352,950	$	191,305	$	161,645	$	—

Summary of the aggregate fair value, gross unrealized gains, gross unrealized losses, realized losses and amortized cost basis of investment portfolio by major security type

	December 31, 2017
	Amortized		Fair		Unrealized				Realized
Available for Sale:	Cost		Value		Gains		Losses		Losses
Municipal bonds	$	32,411	$	31,484	$	—	$	(927)	$	—
Corporate bonds		134,143		133,684		—		(459)		—
Government securities		1,192		1,208		16		—		—
Certificates of deposit		5,245		5,220		—		(25)		—
	$	172,991	$	171,596	$	16	$	(1,411)	$	—

	December 31, 2016
	Amortized		Fair		Unrealized				Realized
Available for Sale:	Cost		Value		Gains		Losses		Losses
Municipal bonds	$	16,046	$	15,206	$	—	$	(840)	$	—
Variable rate demand notes		19,700		19,700		—		—		—
Corporate bonds		122,568		122,298		—		(270)		—
Government securities		2,411		2,426		15		—		—
Certificates of deposit		4,553		4,553		—		—		—
	$	165,278	$	164,183	$	15	$	(1,110)	$	—