Subsequent Events - Additional Information (Detail) - Subsequent Event [Member]	1 Months Ended
	Oct. 31, 2015 USD ($)
4.25% Senior Unsecured Notes Due February 2026 [Member]
Subsequent Event [Line Items]
Proceeds from unsecured notes payable	$ 400,000,000
Debt Instrument, Stated Percentage	4.25%
Debt Instrument Maturity Date	2026-02
Convertible Notes [Member]
Subsequent Event [Line Items]
Convertible notes	$ 350,000,000
Debt instrument redemption, description	Calling the Company’s Convertible Notes for redemption triggered a right of conversion for the holders of the Convertible Notes, whereby such holders may require the Company to deliver to them (i) cash in an amount up to the principal amount of Convertible Notes being converted, and (ii) to the extent that the applicable conversion value exceeds the principal amount of the Convertible Notes being converted, such excess amount in cash, common shares or a combination thereof, at the Company’s election.