Quarterly report pursuant to Section 13 or 15(d)

Derivative Financial Instruments - Additional Information (Detail)

v3.10.0.1
Derivative Financial Instruments - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Jun. 20, 2016
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Mar. 31, 2016
Dec. 31, 2015
Derivative [Line Items]                
Cash flow hedge ineffectiveness   Ineffectiveness was de minimis for the three and nine months ended September 30, 2018 and 2017.   Ineffectiveness was de minimis for the three and nine months ended September 30, 2018 and 2017.        
Repayments of variable rate term notes           $ 225,000,000    
Effective portion of gain (loss) on derivatives net of reclassification to interest expense   $ 100,000 $ 802,000 $ 483,000 $ 2,661,000      
Derivative notional amount             $ 100,000,000 $ 50,000,000
Realized (gain) loss on derivatives net of accumulated other comprehensive loss to interest expense   54,000 758,000 363,000 2,835,000      
Fair value of interest rate swap agreements, asset           205,000    
Interest Rate Swaps Settled in 2018 [Member]                
Derivative [Line Items]                
Effective portion of gain (loss) on derivatives net of reclassification to interest expense       0   $ 0    
Derivative notional amount   100,000,000   100,000,000        
Realized (gain) loss on derivatives net of accumulated other comprehensive loss to interest expense       $ 0        
Senior Term Note Due July 1, 2026 [Member]                
Derivative [Line Items]                
Settlement of forward starting swap agreements $ 9,200,000              
Amortized period on interest expense       10 years        
Interest Expense [Member]                
Derivative [Line Items]                
Realized (gain) loss on derivatives net of accumulated other comprehensive loss to interest expense   (200,000) $ 500,000 $ (300,000) $ 2,100,000      
Unsecured Senior Notes [Member] | Senior Term Note Due July 1, 2026 [Member]                
Derivative [Line Items]                
Debt instrument principal amount $ 600,000,000 $ 600,000,000   $ 600,000,000