Supplemental Guarantor Information Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 29,279	$ 45,939	$ 84,550	$ 52,556
Capital expenditures	(37,482)	(23,288)	(61,461)	(45,460)
Proceeds from the sale of assets	436	7,293	15,455	11,302
Purchase of short term investments and equity securities	(8,948)	(92)	(9,964)	(99)
Sales and maturities of short-term investments	898	648	10,918	1,645
Payments for (Proceeds from) Other Investing Activities	(61)	(1,446)	(1,607)	(2,919)
Payments to Acquire Interest in Subsidiaries and Affiliates	0	0	0	0
CASH USED IN INVESTING ACTIVITIES	(45,157)	(16,885)	(46,659)	(35,531)
Proceeds from Issuance of Unsecured Debt	244,958	0	244,958	0
Proceeds from Issuance of Common Stock	0	73,071	0	73,071
Proceeds from Convertible Debt			244,958
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	(188,931)	(6,712)	(192,157)	(12,683)
Cash payments on gold production royalty	0	(10,461)	0	(19,592)
Proceeds From Repayment Intercompany Borrowings	0	0	0	0
Proceeds from (Payments for) Other Financing Activities	(473)	(448)	(3,720)	(728)
Net Cash Provided by (Used in) Financing Activities	55,554	55,450	49,081	40,068
Effect of exchange rate changes on cash and cash equivalents	329	(302)	884	(216)
Cash and Cash Equivalents, Period Increase (Decrease)	40,005	84,202	87,856	56,877
Cash and cash equivalents at beginning of period	210,033	173,389	162,182	200,714
Cash and cash equivalents at end of period	250,038	257,591	250,038	257,591
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(5,005)	25,384	(9,820)	(3,258)
Capital expenditures	(989)	(88)	(1,308)	(134)
Proceeds from the sale of assets	1	0	8,917	0
Purchase of short term investments and equity securities	(8,948)	(92)	(9,964)	(99)
Sales and maturities of short-term investments	0	0	9,157	500
Payments for (Proceeds from) Other Investing Activities	0	(1,601)	(1,486)	(3,139)
Payments to Acquire Interest in Subsidiaries and Affiliates	(550)	(24,352)	(13,004)	(20,932)
CASH USED IN INVESTING ACTIVITIES	(10,486)	(26,133)	(7,688)	(23,804)
Proceeds from Issuance of Unsecured Debt	244,958
Proceeds from Issuance of Common Stock		73,071		73,071
Proceeds from Convertible Debt			244,958
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	(185,538)	(250)	(185,538)	(500)
Cash payments on gold production royalty		0		0
Proceeds From Repayment Intercompany Borrowings	(6,680)	(5,222)	7,638	(13,101)
Proceeds from (Payments for) Other Financing Activities	(473)	(448)	(3,720)	(728)
Net Cash Provided by (Used in) Financing Activities	52,267	67,151	63,338	58,742
Effect of exchange rate changes on cash and cash equivalents	0	0	0	0
Cash and Cash Equivalents, Period Increase (Decrease)	36,776	66,402	45,830	31,680
Cash and cash equivalents at beginning of period	67,102	61,401	58,048	96,123
Cash and cash equivalents at end of period	103,878	127,803	103,878	127,803
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	14,844	31,117	32,027	52,577
Capital expenditures	(23,937)	(12,932)	(40,912)	(25,722)
Proceeds from the sale of assets	443	41	6,594	4,041
Purchase of short term investments and equity securities	0	0	0	0
Sales and maturities of short-term investments	898	648	1,761	1,145
Payments for (Proceeds from) Other Investing Activities	0	196	0	302
Payments to Acquire Interest in Subsidiaries and Affiliates	823	15,981	753	24,160
CASH USED IN INVESTING ACTIVITIES	(21,773)	3,934	(31,804)	3,926
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	(2,021)	(5,673)	(3,895)	(6,503)
Cash payments on gold production royalty		0		0
Proceeds From Repayment Intercompany Borrowings	10,886	(5,720)	1,561	(30,685)
Proceeds from (Payments for) Other Financing Activities	0	0	0	0
Net Cash Provided by (Used in) Financing Activities	8,865	(11,393)	(2,334)	(37,188)
Effect of exchange rate changes on cash and cash equivalents	0	1	0	5
Cash and Cash Equivalents, Period Increase (Decrease)	1,936	23,659	(2,111)	19,320
Cash and cash equivalents at beginning of period	45,976	29,889	50,023	34,228
Cash and cash equivalents at end of period	47,912	53,548	47,912	53,548
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	24,961	21,384	83,940	31,594
Capital expenditures	(12,556)	(10,268)	(19,241)	(19,604)
Proceeds from the sale of assets	(8)	7,252	(56)	7,261
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	(61)	(41)	(121)	(82)
Payments to Acquire Interest in Subsidiaries and Affiliates	240	0	307	0
CASH USED IN INVESTING ACTIVITIES	(12,385)	(3,057)	(19,111)	(12,425)
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	(1,372)	(789)	(2,724)	(5,680)
Cash payments on gold production royalty		(10,461)		(19,592)
Proceeds From Repayment Intercompany Borrowings	(10,240)	(12,633)	(18,852)	12,201
Proceeds from (Payments for) Other Financing Activities	0	0	0	0
Net Cash Provided by (Used in) Financing Activities	(11,612)	(23,883)	(21,576)	(13,071)
Effect of exchange rate changes on cash and cash equivalents	329	(303)	884	(221)
Cash and Cash Equivalents, Period Increase (Decrease)	1,293	(5,859)	44,137	5,877
Cash and cash equivalents at beginning of period	96,955	82,099	54,111	70,363
Cash and cash equivalents at end of period	98,248	76,240	98,248	76,240
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	(5,521)	(31,946)	(21,597)	(28,357)
Capital expenditures	0	0	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	(513)	8,371	11,944	(3,228)
CASH USED IN INVESTING ACTIVITIES	(513)	8,371	11,944	(3,228)
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	6,034	23,575	9,653	31,585
Proceeds from (Payments for) Other Financing Activities	0	0	0	0
Net Cash Provided by (Used in) Financing Activities	6,034	23,575	9,653	31,585
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
Cash and cash equivalents at end of period	$ 0	$ 0	$ 0	$ 0