Information Concerning Guarantor and Non-Guarantor Subsidiaries - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2017 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