MINERAL PROPERTY INTEREST - Mineral Property Interests (Details) - USD ($) $ in Thousands			3 Months Ended					12 Months Ended
	Jun. 30, 2018	Apr. 19, 2016	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Mineral Property Interests
Purchase price								$ 5,985
Mineral property interests				$ 237,245				242,640	$ 237,245
Impairment charges									50,600	$ 353,736
Amortization of mineral property interests and asset retirement obligations								2,413	1,288	1,236
Nevada
Mineral Property Interests
Impairment charges				7,500	$ 29,700	$ 98,400
Recovery of deferred income tax			$ 10,400	2,200		31,600			31,600
Argentina
Mineral Property Interests
Impairment charges						27,000
Recovery of deferred income tax						3,200
Los Azules Copper Project
Mineral Property Interests
Mineral property interests				191,490				191,490	191,490
Impairment charges				11,400		107,900	$ 120,400
Recovery of deferred income tax				1,300		$ 19,300	$ 22,500
Gold Bar Complex | Nevada
Mineral Property Interests
Impairment charges									20,847	31,391
Tonkin Properties
Mineral Property Interests
Mineral property interests				4,833				4,833	4,833
Tonkin Properties | Nevada
Mineral Property Interests
Impairment charges									14,939	25,435
Other United States Properties | Nevada
Mineral Property Interests
Impairment charges										9,611
El Gallo 1 mine
Mineral Property Interests
Mineral property interests				5,925				8,545	5,925
Amortization of mineral property interests and asset retirement obligations								2,400	1,300	1,300
El Gallo 2 Properties
Mineral Property Interests
Mineral property interests				3,482				5,807	3,482
Impairment charges				2,000
Limo Project | Nevada
Mineral Property Interests
Impairment charges										23,438
North Battle Mountain Complex Located in Nevada, United States | Nevada
Mineral Property Interests
Impairment charges										1,921
North Battle Mountain Properties Located In Nevada United States
Mineral Property Interests
Mineral property interests				785				785	785
North Battle Mountain Properties Located In Nevada United States | Nevada
Mineral Property Interests
Impairment charges									1,443
East Battle Mountain Properties Located In Nevada United States | Nevada
Mineral Property Interests
Impairment charges										4,060
West Battle Mountain Properties Located In Nevada United States | Nevada
Mineral Property Interests
Impairment charges										2,567
Mexico property interests
Mineral Property Interests
Amortization of mineral property interests								1,900	800	800
Amortization of capitalized asset retirement costs									500	500
Gold Bar Project
Mineral Property Interests
Mineral property interests				$ 30,730				31,180	30,730
Royalty
Mineral Property Interests
Required payment of gross revenue less allowable deductions to the tiered net smelter return royalty on the El Gallo 1 Mine (as a percent)		3.50%
Eventually reduced percentage of required payment		1
Purchase price	$ 1,000	$ 5,300
Total purchase price at closing		6,300
Royalty | Non-current other liabilities
Mineral Property Interests
Purchase price								1,000
Royalty | El Gallo 1 mine
Mineral Property Interests
Additional to mineral properties		5,100
Royalty | El Gallo 2 Properties
Mineral Property Interests
Additional to mineral properties		$ 1,200
Argentina | Los Azules Copper Project
Mineral Property Interests
Impairment charges									11,399	228,301
Argentina | Other Argentina exploration properties in San Juan, Argentina
Mineral Property Interests
Impairment charges										7,817
Argentina | Cerro Mojon Tenements in Santa Cruz, Argentina
Mineral Property Interests
Impairment charges										1,971
Argentina | La Merced Tenements in Santa Cruz, Argentina
Mineral Property Interests
Impairment charges										1,891
Argentina | Cabeza de Vaca Tenements in Santa Cruz, Argentina
Mineral Property Interests
Impairment charges										877
Argentina | El Trumai Tenements in Santa Cruz, Argentina
Mineral Property Interests
Impairment charges										1,534
Argentina | Martes 13 Tenements in Santa Cruz, Argentina
Mineral Property Interests
Impairment charges										3,568
Argentina | Celestina Tenements in Santa Cruz, Argentina
Mineral Property Interests
Impairment charges										1,753
Argentina | Other Argentina exploration properties in Santa Cruz, Argentina
Mineral Property Interests
Impairment charges										$ 7,601
Mexico
Mineral Property Interests
Amortization of capitalized asset retirement costs								$ 500
Mexico | Property, Plant and Equipment
Mineral Property Interests
Impairment charges									1,972
Mexico | Nevada And Argentina
Mineral Property Interests
Impairment charges									$ 50,600