Note 1 - Description of Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Principal Transactions Revenue [Table Text Block]

	Year Ended December 31,
	2017			2016			2015
Trade revenue	$	1,832		$	2,069		$	2,299
Trade expense		(1,863	)		(1,997	)		(2,188	)
Net trade (loss) income	$	(31	)	$	72		$	111

Property, Plant and Equipment [Table Text Block]

							Estimated
	December 31,						Useful Lives
	2017			2016			(in years)
Property and equipment:
Land	$	50,458		$	44,611
Buildings and improvements		156,924			139,078			7	to	40
Equipment		511,878			471,798			3	to	20
		719,260			655,487
Accumulated depreciation		(368,602	)		(329,394	)
Total property and equipment, net	$	350,658		$	326,093

Schedule of Weighted Average Number of Shares [Table Text Block]

	Year Ended December 31,
	2017		2016		2015
Weighted-average shares outstanding – basic		73,061		71,848		68,330
Weighted-average shares underlying stock options and restricted shares		775		916		657
Weighted-average shares outstanding - diluted		73,836		72,764		68,987

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

	December 31,
	2017			2016
Accumulated balances of items included in accumulated other comprehensive loss:
Increase in pension liability	$	(36,336	)	$	(28,926	)
Income tax benefit		(14,171	)		(11,281	)
Accumulated other comprehensive loss	$	(22,165	)	$	(17,645	)