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Debt - Additional Information (Detail)
 1 Months Ended 12 Months Ended
Jun. 30, 2016
USD ($)
Dec. 10, 2012
USD ($)
Jun. 30, 2016
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Nov. 30, 2012
USD ($)
Disclosure Of Borrowings [Line Items]            
Debt       $ 595,977,000 $ 593,783,000  
Revolving credit facility [member]            
Disclosure Of Borrowings [Line Items]            
Borrowings           $ 375,000,000.0
Net Debt to EBITDA ratio       2.26 0.9  
LIBOR interest plus margin       2.625%    
Loan undrawn standby fee       0.725%    
Loan undrawn standby fee paid $ 2,031,000          
Prepaid loan cost       $ 749,000 $ 1,272,000  
Revolving credit facility [member] | Amended and restated credit agreement [member]            
Disclosure Of Borrowings [Line Items]            
Borrowings 250,000,000   $ 250,000,000      
Additional borrowing capacity $ 100,000,000   $ 100,000,000      
Borrowings maturity     Jun. 13, 2020      
Aggregate unsecured indebtedness       850,000,000    
Secured indebtedness incurred       200,000,000    
Unsecured indebtedness       $ 150,000,000    
Net Debt to EBITDA ratio       3.5    
Minimum EBITDA to Interest ratio       3    
Loan undrawn standby fee paid       $ 0 0  
Senior notes [member]            
Disclosure Of Borrowings [Line Items]            
Borrowings maturity   Dec. 15, 2020        
Notes issued at par value   $ 600,000,000.0        
Debt fixed interest rate   6.125%        
Senior notes issued   $ 589,500,000        
Fair market value of notes issued       550,000,000    
Deferred financing cost       $ 4,023,000 $ 6,217,000