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Senior Notes - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 6 Months Ended
Jul. 31, 2017
May 31, 2017
Jun. 30, 2017
Jun. 30, 2016
Debt Instrument [Line Items]        
Repayment of senior notes     $ 300,000 $ 240,000
4.7% Senior Unsecured Notes Due June 2027 [Member]        
Debt Instrument [Line Items]        
Senior notes issued   $ 450,000    
Debt instrument interest rate   4.70%    
Debt instrument maturity date   2027-06    
Debt instrument, unamortized discount   $ 800    
Debt instrument, issuance costs   $ 3,900    
4.75% Senior Unsecured Notes Due April 2018 [Member] | Subsequent Event [Member]        
Debt Instrument [Line Items]        
Debt instrument interest rate 4.75%      
Debt instrument maturity date 2018-04      
Repayment of senior notes $ 300,000