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Debt - Additional Information (Detail) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Jan. 21, 2013
Debt Instrument [Line Items]        
Line of Credit Facility, Fair Value of Amount Outstanding $ 108,000   $ 135,000  
Line of Credit, Current 108,000   $ 135,000  
Repayments of Lines of Credit 144,000 $ 477,169    
Line of Credit Facility, Maximum Borrowing Capacity $ 300,000      
Minimum        
Debt Instrument [Line Items]        
Debt Instrument, Description of Variable Rate Basis 0.0125      
Line of Credit Facility, Commitment Fee Percentage 0.20%      
Maximum        
Debt Instrument [Line Items]        
Debt Instrument, Description of Variable Rate Basis 0.02      
Line of Credit Facility, Commitment Fee Percentage 0.35%      
Contractual Interest Rate Reduction [Member]        
Debt Instrument [Line Items]        
Debt Instrument, Description of Variable Rate Basis 0.01      
Interest rate increase [Domain]        
Debt Instrument [Line Items]        
Debt Instrument, Description of Variable Rate Basis 0.0025      
Senior Notes Due 2023        
Debt Instrument [Line Items]        
Debt Instrument, Face Amount       $ 275,000
Debt instrument, interest rate       4.50%
Revolving Credit Facility        
Debt Instrument [Line Items]        
Outstanding stand by letters of credit $ 6,800      
Credit facility available to draw 185,200      
Northwest Farm Credit [Domain]        
Debt Instrument [Line Items]        
Line of Credit Facility, Maximum Borrowing Capacity 100,000      
Wells Fargo [Domain]        
Debt Instrument [Line Items]        
Line of Credit Facility, Maximum Borrowing Capacity $ 200,000