INCOME TAXES: - Other (Details) $ in Millions			12 Months Ended
	Dec. 19, 2024 USD ($)	Dec. 18, 2024	Dec. 31, 2024 USD ($) item	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2025 USD ($)
INCOME TAXES
Total cash, cash equivalents and short-term investments			$ 3,503.4
Deferred tax asset			288.4	$ 204.6
State income tax liability			0.0
Withholding taxes due to the tax treaty between the United States and Mexico			0.0
Changes in unrecognized tax benefits
Unrecognized tax benefits, opening balance			111.0	56.0
Gross increases - tax positions in prior period			23.7	50.2	$ 104.2
Gross increases - current-period tax positions			12.9	8.6
Gross decreases - current-period tax positions					(10.7)
Decreases related to settlements with taxing authorities			(62.9)	(15.7)	(37.5)
Lapse in statute of Limitations			12.3	10.8
Foreign Currency Effects			(4.3)	1.1
Increase (decrease) in unrecognized tax benefits			(18.3)	55.0	56.0
Unrecognized tax benefits, ending balance			92.7	111.0	56.0
Amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate			$ 65.6
Number of major tax jurisdictions | item			3
Unrecognized Tax Benefits			$ 92.7	111.0	56.0
Foreign subsidiaries
INCOME TAXES
Total cash, cash equivalents and short-term investments			577.6
Deferred tax asset			100.0
Foreign
Changes in unrecognized tax benefits
Unrecognized tax benefits, ending balance			27.1
Unrecognized Tax Benefits			$ 27.1
Peru
INCOME TAXES
Royalty charge assessed as a percentage of net sales			1.00%
Royalty charges			$ 103.4	84.8	71.4
Provision for royalty tax			57.5	44.6	35.8
Peruvian special mining tax			86.9	71.7	56.4
Changes in unrecognized tax benefits
Unrecognized tax benefits, ending balance			26.1
Accrued interest and penalties included in liability for uncertain tax positions			17.2	19.7
Unrecognized Tax Benefits			$ 26.1
Peru | Forecast
Changes in unrecognized tax benefits
Income tax expected to be paid						$ 34.7
Peru | Minimum
INCOME TAXES
Mining royalty tax (as a percent)			1.00%
Special mine tax (as a percent)			2.00%
Peru | Maximum
INCOME TAXES
Mining royalty tax (as a percent)			12.00%
Special mine tax (as a percent)			8.40%
Mexico
INCOME TAXES
Mining royalty tax (as a percent)	8.50%	7.50%	7.50%
Mining royalty amount			$ 119.5
Additional royalty tax over gross income from sales of gold, silver and platinum (as a percent)	1.00%	0.50%	0.50%
Effect of changes on deferred tax assets and liabilities	$ 1.0
Additional royalty over sales revenue from gold, silver and platinum			$ 1.4
Changes in unrecognized tax benefits
Unrecognized tax benefits, ending balance			0.0
Accrued interest and penalties included in liability for uncertain tax positions			0.0	0.0	$ 0.0
Unrecognized Tax Benefits			$ 0.0
United States
Changes in unrecognized tax benefits
Accrued interest and penalties included in liability for uncertain tax positions				$ 0.2