INVENTORIES: (Details) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Metals at lower of average cost or market:
Finished goods	$ 93,900,000		$ 84,200,000
Work-in-process	349,300,000		305,400,000
Supplies at average cost	306,800,000		304,300,000
Total current inventory	750,005,000		693,942,000
Inventory, long-term:
Leach stockpiles	539,600,000		395,177,000
Leaching costs added as long-term inventory of leachable material	265,500,000	218,700,000
Long-term leaching inventories recognized as cost of sales	$ 118,800,000	$ 82,600,000