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Employee Benefit Plans - Additional Information (Detail) - Pension Plan [Member] - USD ($)
$ in Millions
1 Months Ended 6 Months Ended
Jan. 31, 2018
Jun. 30, 2018
Defined Contribution Plan Disclosure [Line Items]    
Pension plan termination date   May 31, 2017
Payments to acquire annuities $ 52.0  
Corporate General and Administrative Expenses [Member]    
Defined Contribution Plan Disclosure [Line Items]    
Recognized gain due to termination   $ 1.0