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Debt - 6.375% Senior Unsecured Notes Due 2024 - Additional Information (Detail) - 6.375% Senior Unsecured Notes due 2024 [Member] - USD ($)
12 Months Ended
Feb. 22, 2016
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]      
Senior unsecured notes, interest rate   6.375% 6.375%
Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Senior unsecured notes face amount $ 500,000,000    
Senior unsecured notes, maturity date Mar. 01, 2024    
Senior unsecured notes, interest rate 6.375%    
Debt instrument, redemption price percentage 106.375%    
Senior notes, repurchased price percentage on principal amount plus accrued and unpaid interest 101.00%    
Senior unsecured notes, payable term   Interest on the notes is payable on March 1 and September 1 of each year.  
Senior notes, earliest redemption date Mar. 01, 2019    
Senior unsecured notes, redemption description   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.  
Maximum [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Senior unsecured notes, redemption percentage on principal amount 35.00%