Debt - Components of Debt (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total current debt	$ 13,921,000	$ 20,943,000
Total long-term debt	112,000,000	124,801,000
Subordinated debt—affiliate	10,000,000	0
Total debt	125,921,000	145,744,000
Senior Credit Facility
Debt Instrument [Line Items]
Letters of credit issued	$ 61,700,000	$ 47,200,000
Weighted average interest rate on current portion of debt	4.97%	4.61%
Senior Credit Facility | Bridge Loan
Debt Instrument [Line Items]
Total current debt	$ 0	$ 7,500,000
Senior Credit Facility | Acquisition Line
Debt Instrument [Line Items]
Total long-term debt	102,000,000	117,750,000
Note Payable | Note Payable - Verde
Debt Instrument [Line Items]
Total current debt	13,921,000	13,443,000
Total long-term debt	$ 0	$ 7,051,000