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Summary of Significant Accounting Policies - Additional Information 3 (Detail) - USD ($)
3 Months Ended 6 Months Ended
Dec. 31, 2017
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Operations And Summary Of Significant Accounting Policies [Line Items]          
Federal statutory rate   21.00% 35.00% 21.00% 35.00%
Operating losses carryforward indefinitely with no carryback as percentage of taxable income       80.00%  
Interest expense threshold percentage of adjusted taxable income beyond which interest expense is deductible       30.00%  
Deferred federal tax, Remeasurement Rate       21.00%  
Deferred federal tax, Remeasurement Value $ 140,400,000        
Refundable unused AMT credit carryforward, Percentage       50.00%  
Refundable unused alternative minimum tax credit carryforward years       2018 through 2020  
Refundable unused AMT credit carryforward, Valuation Allowance 19,100,000        
Refundable unused AMT credit carryforward, year fully refunded by       2021  
Cumulative common stock ownership change over three year period that would limit federal and state net operating loss carry forwards       50.00%  
Derivative financial instruments, asset $ 1,300,000        
Net Fair Value Presented in the Consolidated Balance Sheet, Liabilities Derivatives - current   $ 230,000   $ 230,000  
Fixed Rate Debt          
Operations And Summary Of Significant Accounting Policies [Line Items]          
Long-term debt, including current portion, Carrying Value   1,200,000,000   1,200,000,000  
Level 2 | Fixed Rate Debt          
Operations And Summary Of Significant Accounting Policies [Line Items]          
Long-term debt, including current portion, Fair Value   1,200,000,000   1,200,000,000  
Fair Value, Measurements, Recurring | Level 3          
Operations And Summary Of Significant Accounting Policies [Line Items]          
Financial assets   0   0  
Financial liabilities   $ 0   $ 0