Debt - Credit Facility - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) Entity ExtensionOptions	Dec. 31, 2014 USD ($)	Jun. 05, 2015 USD ($)
Debt Instrument [Line Items]
Number of wholly owned subsidiaries | Entity	4
Write off of deferred financing costs	$ 1,926,000
$400 Million Term Loan B [Member]
Debt Instrument [Line Items]
Total credit facility	$ 400,000,000	$ 400,000,000
Maturity Date	Jan. 15, 2021	Jan. 15, 2021
Spread rate added to LIBOR	2.75%	2.75%
$400 Million 5% Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes, principal amount	$ 400,000,000
Interest rate of Senior Notes	5.00%
Maturity date	Apr. 15, 2023
Senior Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maturity Date	Jun. 05, 2019
Number of extension options | ExtensionOptions	2
Spread rate added to LIBOR	1.65%
Senior Secured Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Fee to be paid by the company on the average unused portion	0.20%
Senior Secured Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Fee to be paid by the company on the average unused portion	0.30%
Senior Secured Revolving Credit Facility [Member] | $1 Billion Credit Facility [Member]
Debt Instrument [Line Items]
Total credit facility			$ 700,000,000
Senior Secured Term Loan Facility [Member] | $1 Billion Credit Facility [Member]
Debt Instrument [Line Items]
Total credit facility			$ 300,000,000
Write off of deferred financing costs	$ 1,900,000