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Income Taxes - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Income Taxes [Line Items]        
Unrecognized tax benefits   $ 0 $ 0 $ 0
Unrecognized tax interest accrued   0 0 0
Unrecognized tax penalties accrued   $ 0 $ 0 $ 0
Statutory federal income tax rate   35.00% 35.00% 35.00%
Tax Legislation adjustment   $ 102,500,000    
Effective income tax rate benefit   29.70% (35.30%) (35.80%)
Tax Legislation adjustment   65.10%    
Income taxes paid   $ 6,800,000 $ 9,600,000 $ 53,300,000
Scenario, Plan [Member]        
Schedule Of Income Taxes [Line Items]        
Statutory federal income tax rate 21.00%      
2011- 2012 | Minimum        
Schedule Of Income Taxes [Line Items]        
Income tax examination, year under examination   2015 2013  
2011- 2012 | Maximum        
Schedule Of Income Taxes [Line Items]        
Income tax examination, year under examination   2016 2014