Long-Term Debt - Additional Information (Details)		9 Months Ended
	May 17, 2017 USD ($) Bank	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017
Debt Instrument [Line Items]
Credit facility syndication, number of commercial banks | Bank	11
Line of credit facility, expiration date		May 17, 2022
Line of credit facility, maximum borrowing capacity without borrowing base requirement	$ 600,000,000
Line of credit facility, accordion feature, additional revolving credit commitments under existing loan facility	$ 300,000,000
Line of credit facility, interest coverage ratio covenant	300.00%
Line of credit facility, leverage ratio covenant	375.00%
Long-term debt		$ 232,504,000	$ 206,250,000
Number of letters of credit, outstanding		10
Letters of credit outstanding, amount		$ 3,200,000
Line of credit facility, remaining borrowing capacity		364,300,000
Line of credit facility, current borrowing capacity		$ 214,000,000
Long-term debt, weighted average interest rate, at point in time		3.20%		2.70%
Minimum
Debt Instrument [Line Items]
Line of Credit Facility, Committement Fee Unused Capacity	0.13%
Maximum
Debt Instrument [Line Items]
Line of Credit Facility, Committement Fee Unused Capacity	0.25%
Federal Funds Open Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.50%
London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.00%
London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.00%
Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 60,000,000