XML 69 R59.htm IDEA: XBRL DOCUMENT v3.7.0.1
Debt Debt - Additional Information (Details) - USD ($)
6 Months Ended
Jan. 25, 2017
Jun. 30, 2017
Jun. 30, 2016
Apr. 21, 2017
Dec. 31, 2016
Jul. 31, 2015
Debt Instrument [Line Items]            
Proceeds from Issuance of Long-term Debt   $ 404,395,000 $ 0      
Long-term Debt, Gross   1,872,120,000     $ 1,605,462,000  
Unsecured senior notes 2024 [Member]            
Debt Instrument [Line Items]            
Debt Instrument, Face Amount $ 350,000,000          
Proceeds from Issuance of Long-term Debt $ 345,000,000          
Contractual Interest Rate 5.875%          
Convertible debt [Member]            
Debt Instrument [Line Items]            
Debt Instrument, Face Amount   $ 225,000,000     225,000,000 $ 225,000,000
Contractual Interest Rate   4.00%       4.00%
Revolving Credit Facility [Member]            
Line of Credit Facility [Line Items]            
Line of Credit Facility, Remaining Borrowing Capacity   $ 403,700,000        
Line of Credit Facility, Maximum Borrowing Capacity   500,000,000        
Letters of Credit Outstanding, Amount   $ 36,300,000     $ 31,700,000  
Line of Credit Facility, Commitment Fee Percentage   0.50%        
Federal funds rate [Member] | Revolving Credit Facility [Member]            
Line of Credit Facility [Line Items]            
Debt Instrument, Basis Spread on Variable Rate   0.50%        
Eurodollar [Member] | Revolving Credit Facility [Member]            
Line of Credit Facility [Line Items]            
Debt Instrument Basis Spread On Variable Rate Increase Interval Period   1.00%        
Western Interconnect [Member]            
Debt Instrument [Line Items]            
Contractual Interest Rate   2.00%        
Long-term Debt, Gross       $ 54,400,000.0    
Debt Instrument Basis Spread On Variable Rate Increase   0.25%        
Minimum [Member] | Eurodollar [Member] | Revolving Credit Facility [Member]            
Line of Credit Facility [Line Items]            
Debt Instrument, Basis Spread on Variable Rate   1.25%        
Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]            
Line of Credit Facility [Line Items]            
Debt Instrument, Basis Spread on Variable Rate   2.25%        
Maximum [Member] | Eurodollar [Member] | Revolving Credit Facility [Member]            
Line of Credit Facility [Line Items]            
Debt Instrument, Basis Spread on Variable Rate   1.75%        
Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]            
Line of Credit Facility [Line Items]            
Debt Instrument, Basis Spread on Variable Rate   2.75%        
Broadview Project [Member]            
Debt Instrument [Line Items]            
Current portion of long-term debt including accrued interest       $ 51,200,000