Subsequent Events - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
	Feb. 22, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Senior unsecured notes, payable term		Interest on the notes will be payable on March 1 and September 1 of each year
Senior unsecured notes, redemption description		We may redeem some or all of the notes at any time prior to March 1, 2019 at a “make whole” redemption price. On or after March 1, 2019, we may redeem some or all of the notes at a premium that will decrease over time. In addition, at any time prior to March 1, 2019, we may redeem up to 35% of the notes at a redemption price equal to 106.375% of the aggregate principal amount thereof, plus accrued and unpaid interest thereon, using proceeds from one or more equity offerings. In the event of a change in control, each holder of the notes may require us to repurchase some or all of the notes at a repurchase price equal to 101% of the aggregate principal amount of the notes plus accrued and upaid interest to the date of purchase.
Subsequent Event [Member]
Subsequent Event [Line Items]
Senior unsecured notes face amount	$ 500
Senior unsecured notes commencing date of payment	Sep. 01, 2016
Senior unsecured notes, interest rate	6.375%
Debt instrument, maturity date	Mar. 01, 2024
Senior notes, repurchase price percentage on principal amount plus accrued and unpaid interest	101.00%
Senior notes, earliest redemption date	Mar. 01, 2019
Debt instrument, redemption price percentage	106.375%
Subsequent Event [Member] | Maximum [Member]
Subsequent Event [Line Items]
Senior unsecured notes, redemption price percentage	35.00%