Long-Term Debt - Additional Information (Details)		9 Months Ended
	May 11, 2017 USD ($) Bank	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016
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%
Long-term debt, excluding current maturities		$ 230,080,000	$ 259,389,000
Number of letters of credit, outstanding		12
Letters of credit outstanding, amount		$ 3,700,000
Line of credit facility, remaining borrowing capacity		366,200,000
Line of credit facility, current borrowing capacity		$ 227,700,000
Long-term debt, weighted average interest rate, at point in time		2.70%		2.50%
Federal Funds Effective Swap 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	1.00%