Debt and Letters of Credit - Narrative (Details) - USD ($)			12 Months Ended
	Jul. 17, 2017	Mar. 03, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 01, 2018	Jan. 01, 2018	Sep. 18, 2017	Sep. 17, 2017	Apr. 05, 2017
Line of Credit Facility and Term Loan [Line Items]
Incurred and capitalized direct cost			$ 157,000	$ 1,144,000	$ 0
Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Incurred and capitalized direct cost		$ 1,144,000
Cost related to line of credit		884,000
Cost related to long-term debt		$ 260,000
Amortization of capitalization costs			263,000	202,000
Seasonal borrowing base	$ 15,000,000
Amendment and arrangement fees	145,000
Line of credit facility, commitment fee amount			$ 129,000	65,000
Mandatory prepayment portion of term loans percentage			25.00%
Prepayment amount			$ 12,404,000	4,299,000
Maximum | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Leverage ratio		350.00%
Minimum | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Leverage ratio		110.00%
Line of Credit | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Line of credit facility, maximum borrowing capacity	135,000,000	$ 85,000,000
Debt instrument, term		60 months
Line of credit fee percentage		0.20%	2.21%
Line of credit facility, outstanding balance			$ 23,475,000	$ 31,307,000						$ 2,000,000
Debt covenants, maximum other loans allowable	8,000,000
Weighted average interest rate on all outstanding borrowings			3.30%	2.21%
Line of Credit | Security Agreement, Balance Accruing At 3.00%
Line of Credit Facility and Term Loan [Line Items]
Line of credit fee percentage			3.00%
Line of credit facility, outstanding balance			$ 20,000,000
Line of Credit | Security Agreement, Balance Accruing At 5.00%
Line of Credit Facility and Term Loan [Line Items]
Line of credit fee percentage			5.00%
Line of credit facility, outstanding balance			$ 3,475,000
Line of Credit | Base Rate | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Interest rate, stated percentage		0.50%
Line of Credit | London Interbank Offered Rate (LIBOR) | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Interest rate, stated percentage		1.50%
Term Loan | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Line of credit facility, maximum borrowing capacity		$ 25,000,000
Debt instrument, term		48 months
Line of credit facility principal payment		$ 521,000
Term loan, interest rate (as a percent)			3.38%	2.50%
Effective interest rate			3.01%	3.16%
Term Loan | Base Rate | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Interest rate, stated percentage		1.00%
Term Loan | London Interbank Offered Rate (LIBOR) | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Interest rate, stated percentage		2.00%
Letter of Credit | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Line of credit facility, maximum borrowing capacity	$ 40,000,000	$ 7,500,000						$ 25,000,000
Fronting fee		0.125%
Letters of credit outstanding amount									$ 10,000,000
Term loan, interest rate (as a percent)								1.625%
Line of credit facility, commitment fee amount			$ 157,000
Increase in accrued interest			$ 147,000
Scenario, Forecast | Line of Credit | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Line of credit facility, maximum borrowing capacity						$ 100,000,000
Subsequent Event | Line of Credit | Credit and Security Agreement
Line of Credit Facility and Term Loan [Line Items]
Line of credit facility, maximum borrowing capacity							$ 110,000,000