Long-Term Debt - Additional Information (Details)		12 Months Ended
	May 17, 2017 USD ($) Bank	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
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
New syndicated borrowings used to pay off or pay down borrowings from syndicate members	106,000,000
Line of credit facility, maximum borrowing capacity	$ 60,000,000
Line of credit facility, interest coverage ratio covenant	300.00%
Line of credit facility, leverage ratio covenant	375.00%
Line of credit facility, interest rate during period		0.15%	0.15%
Line of credit facility, remaining borrowing capacity		$ 396,300,000
Line of credit facility, current borrowing capacity		284,300,000
Debt issuance costs, net		6,900,000	$ 6,900,000
Accumulated amortization, debt issuance costs		5,200,000	4,700,000
Amortization of debt issuance costs		$ 510,000	$ 673,000	$ 532,000
Number of letters of credit, outstanding		11	12
Letters of credit outstanding, amount		$ 3,300,000	$ 3,700,000
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)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.25%
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%