Debt - Schedule of Debt (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,872,120	$ 1,605,462
Debt Instrument, Unamortized Discount (Premium), Net	(14,791)	(17,019)
Unamortized financing costs	(30,684)	(24,771)
Total debt, net	1,826,645	1,563,672
Revolving credit facility	60,000	180,000
Current portion of long-term debt, net	54,975	48,716
Long-term debt, less current portion	1,711,670	1,334,956
Revolver credit facility [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 60,000	180,000
Effective Interest Rate	3.46%
Maturity	December 2018
Convertible senior notes 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 225,000	225,000
Contractual Interest Rate	4.00%
Effective Interest Rate	6.60%
Maturity	July 2020
Unsecured senior notes 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 350,000	0
Contractual Interest Rate	5.88%
Effective Interest Rate	5.88%
Maturity	February 2024
E1 Arrayan EKF term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 101,984	103,904
Contractual Interest Rate	5.56%
Effective Interest Rate	5.56%
Maturity	March 2029
Santa Isabel term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 105,953	107,090
Contractual Interest Rate	4.57%
Effective Interest Rate	4.57%
Maturity	September 2033
Ocotillo commercial term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 188,906	193,257
Contractual Interest Rate	2.90%
Effective Interest Rate	3.82%
Maturity	August 2020
Lost Creek term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 100,145	103,846
Contractual Interest Rate	3.07%
Effective Interest Rate	6.51%
Maturity	September 2027
El Arrayan commercial term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 92,713	94,458
Contractual Interest Rate	4.17%
Effective Interest Rate	5.70%
Maturity	March 2029
Spring Valley term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 127,445	130,658
Contractual Interest Rate	3.05%
Effective Interest Rate	5.19%
Maturity	June 2030
Ocotillo development term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 101,200	102,300
Contractual Interest Rate	3.25%
Effective Interest Rate	4.42%
Maturity	August 2033
St. Joseph term loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 168,016	162,356
Contractual Interest Rate	2.70%
Effective Interest Rate	3.86%
Maturity	November 2033
Western Interconnect [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 54,395	0
Contractual Interest Rate	3.05%
Effective Interest Rate	3.97%
Maturity	April 2027
Hatchet Ridge financing lease obligation [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 196,363	$ 202,593
Contractual Interest Rate	1.43%
Effective Interest Rate	1.43%
Maturity	December 2032

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Name Accounting Standards Codification
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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

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Amount, after accumulated amortization, of debt discount (premium).

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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