Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments - Additional Information (Detail)

v3.8.0.1
Derivative Financial Instruments - Additional Information (Detail)
3 Months Ended 12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Agreement
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Mar. 31, 2016
USD ($)
Derivative [Line Items]          
Cash flow hedge ineffectiveness   Ineffectiveness was de minimis in 2017, 2016, and 2015.      
Notional amount of variable rate debt swapped $ 1,742,674,000 $ 1,742,674,000      
Number of interest rate swap agreements | Agreement   1      
Unsecured term note 1,625,000,000 $ 1,625,000,000 $ 1,400,000,000    
Repayments of variable rate term notes 225,000,000 225,000,000 150,000,000    
Gains or losses related to terminated interest rate swaps included in AOCL   13,888,000 (7,060,000) $ (1,410,000)  
Derivative notional amount       50,000,000 $ 100,000,000
Realized loss reclassified from accumulated other comprehensive loss to interest expense   (13,185,000) (5,044,000) (5,229,000)  
Fair value of interest rate swap agreements, asset 205,000 205,000      
Fair value of interest rate swap agreements, liability     13,015,000    
Senior Term Note Due July 1, 2026 [Member]          
Derivative [Line Items]          
Unsecured term note 600,000,000 600,000,000 600,000,000    
Settlement of forward starting swap agreements   $ 9,200,000      
Amortized period on interest expense   10 years      
Interest Expense [Member]          
Derivative [Line Items]          
Settlement of terminated interest rate swap agreements   $ 9,600,000      
Realized loss reclassified from accumulated other comprehensive loss to interest expense   12,300,000 $ 4,600,000 $ 5,200,000  
Interest Rate Swap [Member]          
Derivative [Line Items]          
Unsecured term note 100,000,000 100,000,000      
Gains or losses related to terminated interest rate swaps included in AOCL   0      
Derivative notional amount $ 100,000,000 $ 100,000,000