Information Concerning Guarantor and Non-Guarantor Subsidiaries - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2015 USD ($) Entity	Dec. 31, 2014 USD ($)
Condensed Financial Statements, Captions [Line Items]
Number of wholly owned subsidiaries	4
Ownership percentage in subsidiaries	100.00%
Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Number of wholly owned subsidiaries	4
$350 Million Senior Notes at 5% Interest [Member]
Condensed Financial Statements, Captions [Line Items]
Interest rate of Senior Notes	5.00%	5.00%
Senior notes, principal amount | $	$ 350,000,000	$ 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