Note 9 - Debt, Credit Facility and Leases (Details Textual) $ in Thousands, shares in Millions, $ in Millions				1 Months Ended		12 Months Ended
	Feb. 16, 2026	Jul. 09, 2020 CAD ($)	Mar. 19, 2020 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2019 CAD ($) shares	Feb. 15, 2026	Feb. 15, 2025	Feb. 15, 2024	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 09, 2020 USD ($)	Jul. 09, 2020 CAD ($)	Feb. 19, 2020 USD ($)	Jul. 31, 2018 USD ($)	Mar. 05, 2018 CAD ($)	May 31, 2016 USD ($)
Proceeds from Issuance of Long-term Debt, Total									$ 0	$ 716,327	$ 279,500
Payments of Debt Issuance Costs									116	1,356	976
Paid-in-Kind Prepayment of Debt Fee									0	0	2,855
Finance Lease, Liability, Total									13,388	15,800
Finance Lease, Liability, Current									5,612	6,491
Finance Lease, Liability, Noncurrent									7,776	9,274
Finance Lease, Right-of-Use Asset, Amortization									8,900	7,400	5,900
Finance Lease, Interest Expense									600	600	700
Finance Lease, Liability, Payment, Due, Total									14,231
Finance Lease, Liability, Undiscounted Excess Amount									$ 843
Finance Lease, Weighted Average Remaining Lease Term (Year)									2 years
Finance Lease, Weighted Average Discount Rate, Percent									6.30%
Operating Lease, Weighted Average Discount Rate, Percent									5.80%
Operating Lease, Liability, Total									$ 12,436	10,600
Operating Lease, Liability, Current									2,486	3,008
Operating Lease, Liability, Noncurrent									9,950	7,634
Operating Lease, Right-of-Use Asset									12,435	10,628
Operating Lease, Expense									3,900	7,200	7,500
Lessee, Operating Lease, Liability, to be Paid, Total									$ 15,783
Operating Lease, Weighted Average Remaining Lease Term (Year)									6 years 6 months
Properties, Plants, Equipment and Mineral Interests [Member]
Finance Lease, Right-of-Use Asset, after Accumulated Amortization, Total									$ 18,300	22,300
Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity															$ 250,000		$ 100,000
Letters of Credit Outstanding, Amount									17,300
Long-term Line of Credit, Total									0	0
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]
Interest Expense, Debt, Total									35,400	40,200	36,300
Long-term Debt, Total									$ 508,095	$ 507,242
Senior Notes [Member] | The 2028 Senior Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage									7.25%	7.25%				7.25%
Debt Instrument, Face Amount														$ 475,000
Proceeds from Issuance of Long-term Debt, Total			$ 469,500
Underwriting Discount on Senior Notes														1.16%
Debt Instrument, Unamortized Discount, Total														$ 5,500
Debt Instrument, Redemption Price, Percentage, Net of Cash Proceeds of Equity Offerings									35.00%
Debt Instrument, Redemption Price, Percentage, Including Accrued and Unpaid Interest									101.00%
Long-term Debt, Total									$ 469,448	$ 468,538
Senior Notes [Member] | The 2028 Senior Notes [Member] | Forecast [Member]
Debt Instrument, Redemption Price, Percentage	100.00%					101.813%	103.625%	105.438%
Senior Notes [Member] | The 2021 Senior Notes [Member]
Debt Instrument, Unamortized Discount (Premium), Net, Total									1,700
Senior Notes [Member] | IQ Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage												6.515%	6.515%
Debt Instrument, Face Amount												$ 36,800	$ 50.0
Interest Expense, Debt, Total									2,300	900
Debt Instrument, Unamortized Premium, Percentage of Principal												103.65%	103.65%
Debt Instrument, Unamortized Premium, Total													$ 1.8
Debt Instrument, Effective Annual Yield												5.74%	5.74%
Long-term Debt, Total									$ 38,647	$ 38,704			$ 48.2
Debt Instrument, Number of Issuance Installments												4	4
Proceeds from Issuance of Debt		$ 12.5
Payments of Debt Issuance Costs		$ 0.6
Debt Instrument, Covenant, Investment Over Next Four Years													$ 100.0
Series 2018-A Senior Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage																4.68%
Debt Instrument, Face Amount																$ 40.0
Interest Expense, Debt, Total											4,200
Paid-in-Kind Prepayment of Debt Fee											$ 2,900