Summary of Significant Accounting Policies - Additional Information 3 (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Operations And Summary Of Significant Accounting Policies [Line Items]
Federal statutory rate	21.00%
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%
Refundable unused AMT credit carryforward, Percentage	50.00%
Refundable unused alternative minimum tax credit carryforward years	2018 through 2020
Unused AMT credit carryforwards	$ 20,400,000
Net operating loss limitation	$ 3,300,000
Period of increase in net operating loss limitation	5 years
Section 382 limitation recognition period	2018 to 2023
Net operating loss expiration period	20 years
Derivative financial instruments, asset	$ 2,400,000			$ 15,400,000
Long Term Debt
Operations And Summary Of Significant Accounting Policies [Line Items]
Long-term debt, including current portion, Carrying Value	817,800,000
Level 2 | Long Term Debt
Operations And Summary Of Significant Accounting Policies [Line Items]
Long-term debt, including current portion, Fair Value	786,300,000
Fair Value, Measurements, Recurring | Level 3
Operations And Summary Of Significant Accounting Policies [Line Items]
Financial assets	0
Financial liabilities	$ 0
Predecessor
Operations And Summary Of Significant Accounting Policies [Line Items]
Federal statutory rate		21.00%	35.00%