Note 9 - Debt, Credit Facility and Leases (Details Textual) $ in Thousands, shares in Millions, $ in Millions		1 Months Ended		3 Months Ended
	Mar. 19, 2020 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2019 CAD ($) shares	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Jul. 01, 2020	Feb. 19, 2020 USD ($)	Jul. 31, 2018 USD ($)	Mar. 05, 2018 USD ($)	Mar. 05, 2018 CAD ($)	May 31, 2016 USD ($)
Proceeds from Issuance of Long-term Debt, Total				$ 679,500	$ 58,000
Finance Lease, Liability, Total		$ 12,600		11,201
Finance Lease, Liability, Current		5,429		5,391
Finance Lease, Liability, Noncurrent		7,214		5,810
Finance Lease, Right-of-Use Asset, after Accumulated Amortization, Total		20,600		19,100
Finance Lease, Right-of-Use Asset, Amortization				1,500	1,600
Finance Lease, Interest Expense				100	200
Finance Lease, Liability, Payment, Due, Total				11,861
Finance Lease, Liability, Undiscounted Excess Amount				$ 660
Finance Lease, Weighted Average Remaining Lease Term (Year)				1 year 8 months 12 days
Finance Lease, Weighted Average Discount Rate, Percent				5.90%
Operating Lease, Weighted Average Discount Rate, Percent				6.50%
Operating Lease, Liability, Total		16,400		$ 14,931
Operating Lease, Liability, Current		5,580		4,792
Operating Lease, Liability, Noncurrent		10,818		10,139
Operating Lease, Right-of-Use Asset		$ 16,381		14,909
Operating Lease, Expense				1,900	2,100
Lessee, Operating Lease, Liability, to be Paid, Total				$ 16,082
Operating Lease, Weighted Average Remaining Lease Term (Year)				4 years 7 months 6 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								$ 250,000
Line of Credit Facility, Amount Available for Refinance											$ 100,000
Letters of Credit Outstanding, Amount				$ 28,700
Long-term Line of Credit, Total				210,000
Revolving Credit Facility [Member] | Forecast [Member]
Leverage Ratio						4.00
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								4.00%
Conversion of Series 2018A Senior Notes Into Common Stock [Member]
Debt Conversion, Converted Instrument, Shares Issued (in shares) | shares		10.7	10.7
Debt Conversion, Converted Instrument, Amount		$ 33,500	$ 43.8
Senior Notes [Member] | The 2028 Senior Notes [Member]
Debt Instrument, Face Amount							$ 475,000
Debt Instrument, Interest Rate, Stated Percentage							7.25%
Proceeds from Issuance of Long-term Debt, Total	$ 469,500
Long-term Debt, Gross				475,000
Underwriting Discount on Senior Notes							1.16%
Debt Instrument, Unamortized Discount, Total							$ 5,500
Debt Instrument, Unamortized Discount, Total				6,000
Long-term Debt, Total				$ 469,000
Debt Instrument, Redemption Price, Percentage				100.00%
Debt Instrument, Redemption Price, Percentage, Net of Cash Proceeds of Equity Offerings				35.00%
Debt Instrument, Redemption Price, Percentage				101.00%
Senior Notes [Member] | The 2021 Senior Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage		6.875%
Long-term Debt, Gross		$ 506,500
Amortization of Debt Discount (Premium)	$ 1,700
Long-term Debt, Total		504,700
Debt Instrument, Unamortized Discount (Premium), Net, Total		$ 1,800
Senior Notes [Member] | The 2028 Senior Notes and 2021 Senior Notes [Member]
Interest Expense, Debt, Total				$ 13,700	9,100
Series 2018-A Senior Notes [Member]
Debt Instrument, Face Amount									$ 30,800	$ 40.0
Debt Instrument, Interest Rate, Stated Percentage									4.68%	4.68%
Debt Instrument, Unamortized Discount, Total										$ 0.2
Interest Expense, Debt, Total					$ 400
Debt Instrument, Issuance, Discount Rate									0.58%	0.58%