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Information Concerning Guarantor and Non-Guarantor Subsidiaries - Additional Information (Detail)
6 Months Ended
Jun. 30, 2018
USD ($)
Entity
Condensed Financial Statements, Captions [Line Items]  
Number of wholly owned subsidiaries | Entity 4
Ownership percentage in subsidiaries 100.00%
$350 Million 5% Senior Notes [Member]  
Condensed Financial Statements, Captions [Line Items]  
Interest rate of Senior Notes 5.00%
Senior notes, principal amount $ 350,000,000
$400 Million 5% Senior Notes [Member]  
Condensed Financial Statements, Captions [Line Items]  
Interest rate of Senior Notes 5.00%
Senior notes, principal amount $ 400,000,000