Supplemental Guarantor Information Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 29,432		$ 47,812	$ 113,982	$ 100,368
Capital expenditures	(29,461)		(25,627)	(90,922)	(71,087)
Payments to Acquire Businesses, Net of Cash Acquired	0	$ 0	(1,427)		(1,427)
Proceeds from the sale of assets	1,083		4,802	16,538	16,104
Purchase of short term investments and equity securities	(3,595)		(21)	(13,559)	(120)
Sales and maturities of short-term investments	403		5,432	11,321	7,077
Payments for (Proceeds from) Other Investing Activities	(5,850)		(1,299)	(7,457)	(4,218)
Payments to Acquire Interest in Subsidiaries and Affiliates	0		0	0	0
CASH USED IN INVESTING ACTIVITIES	(37,420)		(18,140)	(84,079)	(53,671)
Proceeds from Issuance of Unsecured Debt	(2,257)		0	242,701	0
Proceeds from Issuance of Common Stock	0		49,513	0	122,584
Proceeds from Convertible Debt				242,701
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	(3,344)		(107,868)	(195,501)	(120,551)
Cash payments on gold production royalty	0		(7,563)	0	(27,155)
Proceeds From Repayment Intercompany Borrowings	0		0	0	0
Proceeds from (Payments for) Other Financing Activities	(6)		1,051	(3,726)	323
Net Cash Provided by (Used in) Financing Activities	(5,607)		(64,867)	43,474	(24,799)
Effect of exchange rate changes on cash and cash equivalents	(222)		121	662	(95)
Cash and Cash Equivalents, Period Increase (Decrease)	(13,817)		(35,074)	74,039	21,803
Cash and cash equivalents at beginning of period	250,038	162,182	257,591	162,182	200,714
Cash and cash equivalents at end of period	236,221		222,517	236,221	222,517
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(8,682)		101,581	(18,502)	98,323
Capital expenditures	(318)		(62)	(1,626)	(196)
Payments to Acquire Businesses, Net of Cash Acquired			0		0
Proceeds from the sale of assets	0		2	8,917	2
Purchase of short term investments and equity securities	(3,594)		(5)	(13,558)	(104)
Sales and maturities of short-term investments	0		2	9,157	501
Payments for (Proceeds from) Other Investing Activities	(5,783)		(1,245)	(7,269)	(4,383)
Payments to Acquire Interest in Subsidiaries and Affiliates	3,433		(117,911)	(9,571)	(138,843)
CASH USED IN INVESTING ACTIVITIES	(6,262)		(119,219)	(13,950)	(143,023)
Proceeds from Issuance of Unsecured Debt	(2,257)
Proceeds from Issuance of Common Stock			49,513		122,584
Proceeds from Convertible Debt				242,701
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	0		(104,165)	(185,538)	(104,665)
Cash payments on gold production royalty			0		0
Proceeds From Repayment Intercompany Borrowings	9,266		39,297	16,904	26,196
Proceeds from (Payments for) Other Financing Activities	(6)		1,051	(3,726)	323
Net Cash Provided by (Used in) Financing Activities	7,003		(14,304)	70,341	44,438
Effect of exchange rate changes on cash and cash equivalents	0		0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	(7,941)		(31,942)	37,889	(262)
Cash and cash equivalents at beginning of period	103,878	58,048	127,803	58,048	96,123
Cash and cash equivalents at end of period	95,937		95,861	95,937	95,861
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	27,407		48,791	59,434	101,368
Capital expenditures	(23,016)		(12,550)	(63,928)	(38,272)
Payments to Acquire Businesses, Net of Cash Acquired			0		0
Proceeds from the sale of assets	76		560	6,670	4,601
Purchase of short term investments and equity securities	(1)		(16)	(1)	(16)
Sales and maturities of short-term investments	403		5,430	2,164	6,576
Payments for (Proceeds from) Other Investing Activities	0		(7)	0	294
Payments to Acquire Interest in Subsidiaries and Affiliates	7,144		1,356	7,897	25,516
CASH USED IN INVESTING ACTIVITIES	(15,394)		(5,227)	(47,198)	(1,301)
Proceeds from Issuance of Unsecured Debt	0
Proceeds from Issuance of Common Stock			0		0
Proceeds from Convertible Debt				0
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	(1,894)		(2,498)	(5,789)	(9,001)
Cash payments on gold production royalty			0		0
Proceeds From Repayment Intercompany Borrowings	(12,370)		(42,679)	(10,809)	(73,364)
Proceeds from (Payments for) Other Financing Activities	0		0	0	0
Net Cash Provided by (Used in) Financing Activities	(14,264)		(45,177)	(16,598)	(82,365)
Effect of exchange rate changes on cash and cash equivalents	3		0	3	5
Cash and Cash Equivalents, Period Increase (Decrease)	(2,248)		(1,613)	(4,359)	17,707
Cash and cash equivalents at beginning of period	47,912	50,023	53,548	50,023	34,228
Cash and cash equivalents at end of period	45,664		51,935	45,664	51,935
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	9,471		21,586	93,411	53,180
Capital expenditures	(6,127)		(13,015)	(25,368)	(32,619)
Payments to Acquire Businesses, Net of Cash Acquired			(1,427)		(1,427)
Proceeds from the sale of assets	1,007		4,240	951	11,501
Purchase of short term investments and equity securities	0		0	0	0
Sales and maturities of short-term investments	0		0	0	0
Payments for (Proceeds from) Other Investing Activities	(67)		(47)	(188)	(129)
Payments to Acquire Interest in Subsidiaries and Affiliates	(1,311)		0	(1,004)	0
CASH USED IN INVESTING ACTIVITIES	(6,498)		(10,249)	(25,609)	(22,674)
Proceeds from Issuance of Unsecured Debt	0
Proceeds from Issuance of Common Stock			0		0
Proceeds from Convertible Debt				0
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	(1,450)		(1,205)	(4,174)	(6,885)
Cash payments on gold production royalty			(7,563)		(27,155)
Proceeds From Repayment Intercompany Borrowings	(4,926)		(4,209)	(23,778)	7,992
Proceeds from (Payments for) Other Financing Activities	0		0	0	0
Net Cash Provided by (Used in) Financing Activities	(6,376)		(12,977)	(27,952)	(26,048)
Effect of exchange rate changes on cash and cash equivalents	(225)		121	659	(100)
Cash and Cash Equivalents, Period Increase (Decrease)	(3,628)		(1,519)	40,509	4,358
Cash and cash equivalents at beginning of period	98,248	54,111	76,240	54,111	70,363
Cash and cash equivalents at end of period	94,620		74,721	94,620	74,721
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	1,236		(124,146)	(20,361)	(152,503)
Capital expenditures	0		0	0	0
Payments to Acquire Businesses, Net of Cash Acquired			0		0
Proceeds from the sale of assets	0		0	0	0
Purchase of short term investments and equity securities	0		0	0	0
Sales and maturities of short-term investments	0		0	0	0
Payments for (Proceeds from) Other Investing Activities	0		0	0	0
Payments to Acquire Interest in Subsidiaries and Affiliates	(9,266)		116,555	2,678	113,327
CASH USED IN INVESTING ACTIVITIES	(9,266)		116,555	2,678	113,327
Proceeds from Issuance of Unsecured Debt	0
Proceeds from Issuance of Common Stock			0		0
Proceeds from Convertible Debt				0
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	0		0	0	0
Cash payments on gold production royalty			0		0
Proceeds From Repayment Intercompany Borrowings	8,030		7,591	17,683	39,176
Proceeds from (Payments for) Other Financing Activities	0		0	0	0
Net Cash Provided by (Used in) Financing Activities	8,030		7,591	17,683	39,176
Effect of exchange rate changes on cash and cash equivalents	0		0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	0		0	0	0
Cash and cash equivalents at beginning of period	0	$ 0	0	0	0
Cash and cash equivalents at end of period	$ 0		$ 0	$ 0	$ 0