Debt - 2016 Activity - Additional Information (Detail) - USD ($)			3 Months Ended	9 Months Ended
	Jul. 22, 2016	Feb. 22, 2016	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
2026 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes face amount	$ 500,000,000
Senior unsecured notes, payable term				Interest on the notes will be payable on February 1 and August 1 of each year
Senior unsecured notes commencing date of payment	Feb. 01, 2017
Senior unsecured notes, interest rate	5.25%
Senior unsecured notes, maturity date	Aug. 01, 2026
Senior notes, earliest redemption date	Aug. 01, 2021
Senior unsecured notes, redemption description				We may redeem some or all of the notes at any time prior to August 1, 2021 at a “make whole” redemption price. On or after August 1, 2021, we may redeem some or all of the notes at a premium that will decrease over time. In addition, at any time prior to August 1, 2019, we may redeem up to 35% of the notes at a redemption price equal to 105.25% 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 unpaid interest to the date of purchase.
Debt instrument, redemption price percentage	105.25%
Senior notes, repurchased price percentage on principal amount plus accrued and unpaid interest	101.00%
2026 Senior Unsecured Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Senior unsecured notes, redemption percentage on principal amount	35.00%
2011 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes, interest rate					6.875%
Notes redeemed			$ 450,000,000
Debt refinancing charge			22,500,000
Redemption premium			$ 15,500,000
Revolving Credit Facility [Member] | 2016 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Senior unsecured notes face amount		$ 500,000,000
Senior unsecured notes, payable term				Interest on the notes is payable on March 1 and September 1 of each year
Senior unsecured notes commencing date of payment		Sep. 01, 2016
Senior unsecured notes, interest rate		6.375%
Senior unsecured notes, maturity date		Mar. 01, 2024
Senior notes, earliest redemption date		Mar. 01, 2019
Senior unsecured notes, redemption description				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 unpaid interest to the date of purchase.
Debt instrument, redemption price percentage		106.375%
Senior notes, repurchased price percentage on principal amount plus accrued and unpaid interest		101.00%
Revolving Credit Facility [Member] | 2016 Senior Unsecured Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Senior unsecured notes, redemption percentage on principal amount		35.00%