Annual report pursuant to Section 13 and 15(d)

Subsequent Events (Details)

v3.10.0.1
Subsequent Events (Details)
 1 Months Ended 2 Months Ended 12 Months Ended
Feb. 28, 2019
MMBTU
$ / MMBTU
Feb. 28, 2019
$ / MMBTU
shares
Dec. 31, 2018
shares
Jan. 31, 2019
USD ($)
May 31, 2018
USD ($)
Jan. 31, 2018
USD ($)
Derivative [Line Items]            
Stock repurchase program, authorized amount | $         $ 200,000,000 $ 100,000,000
Stock repurchased and retired during period (shares) | shares     20,700,000      
Subsequent event            
Derivative [Line Items]            
Stock repurchase program, authorized amount | $       $ 400,000,000.0    
Stock repurchased and retired during period (shares) | shares   0        
Natural Gas Basis Swap 2020 | Subsequent event            
Derivative [Line Items]            
Daily Volume (MMBtu/day) | MMBTU 10,000          
Differential of MMBtu (in usd per MMbtu) | $ / MMBTU 0.535 0.535