Long-Term Debt - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Principal amount	$ 695,000,000	$ 625,000,000
Debt, fair value	596,000,000	594,400,000
Purchase of equipment	1,800,000
Maximum Credit Amount, Maximum Commitments That Could Be Elected By Lenders	$ 1,500,000,000
Minimum
Debt Instrument [Line Items]
Revolving credit facility interest rate percent above LIBOR alternate interest rate	0.50%
Commitment fee percentage	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%
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
Debt, Weighted Average Interest Rate	4.00%
Letters of credit issued amount	$ 26,000,000
Line of credit facility, remaining borrowing capacity	404,000,000
Principal amount	70,000,000	0
7.0% Senior Notes
Debt Instrument [Line Items]
Principal amount	$ 350,000,000	350,000,000
Debt, stated interest rate	7.00%
Debt, fair value	$ 332,700,000	329,700,000
8.75% Senior Notes
Debt Instrument [Line Items]
Principal amount	$ 275,000,000	275,000,000
Debt, stated interest rate	8.75%
Debt, fair value	$ 263,300,000	264,700,000
Lease Financing Obligation
Debt Instrument [Line Items]
Principal amount	$ 0	1,859,000
Debt, fair value		$ 1,800,000