Note 9 - Debt, Credit Facility and Leases (Details Textual) $ in Thousands, $ in Millions			9 Months Ended		12 Months Ended
	May 01, 2019	Apr. 12, 2013 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2014 USD ($)	Jul. 01, 2020	Apr. 01, 2020	Jan. 01, 2020	Dec. 31, 2019	Oct. 01, 2019	Jul. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Mar. 05, 2018 USD ($)	Mar. 05, 2018 CAD ($)	May 31, 2016 USD ($)
Letters of Credit Outstanding, Amount			$ 38,500
Finance Lease, Liability, Total			14,275										$ 13,100
Finance Lease, Liability, Current			5,704										5,264
Finance Lease, Liability, Noncurrent			8,569										7,871
Finance Lease, Right-of-Use Asset			21,400										20,000
Finance Lease, Right-of-Use Asset, Amortization			5,100
Finance Lease, Interest Expense			600
Finance Lease, Liability, Payment, Due, Total			15,243
Finance Lease, Liability, Undiscounted Excess Amount			$ 968
Finance Lease, Weighted Average Remaining Lease Term			1 year 10 months 24 days
Operating Lease, Liability, Total			$ 17,330									$ 22,400
Operating Lease, Liability, Current			5,864										0
Operating Lease, Liability, Noncurrent			11,466										0
Operating Lease, Right-of-Use Asset			17,313									$ 22,400	$ 0
Operating Lease, Expense			5,700
Lessee, Operating Lease, Liability, Payments, Due, Total			$ 17,393
Operating Lease, Weighted Average Remaining Lease Term			4 years 8 months 12 days
Minimum [Member]
Lessee, Operating Lease, Discount Rate			5.00%
Maximum [Member]
Lessee, Operating Lease, Discount Rate			6.50%
Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity											$ 150,000			$ 250,000			$ 100,000
Leverage Ratio			6.50
Proceeds from Lines of Credit, Total			$ 50,000
Revolving Credit Facility [Member] | Subsequent Event [Member]
Leverage Ratio										6.00
Revolving Credit Facility [Member] | Forecast [Member]
Leverage Ratio						4.00	5.00	5.50	6.00
Letter of Credit [Member]
Letter of Credit Outstanding, Fronting Fee														0.20%
Letter of Credit [Member] | Minimum [Member]
Letter of Credit, Participation Fee, Percent														2.25%
Letter of Credit [Member] | Maximum [Member]
Letter of Credit, Participation Fee, Percent														3.25%
Senior Notes [Member]
Debt Instrument, Face Amount		$ 500,000
Payment for Pension Benefits					$ 6,500
Proceeds from Issuance of Senior Long-term Debt		$ 490,000
Underwriting Discount on Senior Notes		2.00%
Debt Instrument, Unamortized Discount, Total		$ 10,000	2,100
Debt Instrument, Interest Rate, Stated Percentage		6.875%
Interest Expense, Debt, Total			27,200	$ 27,200
Debt Instrument, Redemption Price, Percentage	100.00%	101.00%
Series 2018-A Senior Notes [Member]
Debt Instrument, Face Amount															$ 30,800	$ 40.0
Debt Instrument, Unamortized Discount, Total																$ 0.2
Debt Instrument, Interest Rate, Stated Percentage															4.68%	4.68%
Interest Expense, Debt, Total			$ 1,100	$ 1,100
Debt Instrument, Issuance, Discount Rate															0.58%	0.58%