Long-Term Debt - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.20%	4.10%
Principal amount	$ 775,000,000	$ 775,000,000		$ 625,000,000
Debt, fair value	597,300,000	597,300,000		594,400,000
Purchase of equipment			$ 1,800,000
Maximum Credit Amount, Maximum Commitments That Could Be Elected By Lenders	$ 1,500,000,000	$ 1,500,000,000
Minimum
Debt Instrument [Line Items]
Revolving credit facility interest rate percent above LIBOR alternate interest rate		0.50%
Commitment fee percentage	0.375%	0.375%
Revolving Credit Facility Interest Rate Percent Above Libor		1.50%
Maximum
Debt Instrument [Line Items]
Revolving credit facility interest rate percent above LIBOR alternate interest rate		1.50%
Commitment fee percentage	0.50%	0.50%
Revolving Credit Facility Interest Rate Percent Above Libor		2.50%
Amended Credit Facility
Debt Instrument [Line Items]
Debt instrument, maturity date		Sep. 14, 2023
Line of credit facility, maximum borrowing capacity	$ 500,000,000.0	$ 500,000,000.0
Letters of credit issued amount	26,000,000.0	26,000,000.0
Line of credit facility, remaining borrowing capacity	324,000,000.0	324,000,000.0
Principal amount	150,000,000	150,000,000		0
7.0% Senior Notes
Debt Instrument [Line Items]
Principal amount	$ 350,000,000	$ 350,000,000		350,000,000
Debt, stated interest rate	7.00%	7.00%
Debt, fair value	$ 332,600,000	$ 332,600,000		329,700,000
8.75% Senior Notes
Debt Instrument [Line Items]
Principal amount	$ 275,000,000	$ 275,000,000		275,000,000
Debt, stated interest rate	8.75%	8.75%
Debt, fair value	$ 264,700,000	$ 264,700,000		264,700,000
Lease Financing Obligation
Debt Instrument [Line Items]
Principal amount	$ 0	$ 0		1,859,000
Debt, fair value				$ 1,800,000