Long-Term Debt and Credit Facility - Additional Information (Details)			3 Months Ended	9 Months Ended
	Aug. 31, 2018 USD ($)	Feb. 27, 2018	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Mar. 12, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2017 USD ($)	Oct. 31, 2015 USD ($)
Debt Instrument [Line Items]
Fees				$ 2,500,000
Up front lending fees				900,000
Third party arrangement fees				1,600,000
Third-party notes and bank debt held			$ 800,000	800,000		$ 900,000
Repayments of lines of credit				(19,000,000)
Debt designated as third-party debt						7,800,000
Long-term debt, fair value			305,600,000	305,600,000		356,000,000
2015 Interest Rate Swap
Debt Instrument [Line Items]
Interest rate at period end								3.74%
Notional amount								$ 262,500,000
Fixed interest rate								1.46%
2018 Interest Rate Swap
Debt Instrument [Line Items]
Notional amount					$ 170,600,000.0
Portion of amortization of term loan					$ 170,600,000
Fixed interest rate					2.937%
Term Loan [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity			308,400,000.0	308,400,000.0
2015 Credit Facility
Debt Instrument [Line Items]
Senior secured credit facility								$ 650,000,000
Maximum borrowing capacity							$ 350,000,000
Secured debt outstanding			288,800,000	288,800,000		308,400,000
Proceeds from line of credit, net				19,000,000
Letters of credit issued and outstanding			$ 29,300,000	$ 29,300,000
Line of credit						$ 38,000,000
Portion of amortization of term loan								$ 262,500,000
Initial maximum financial leverage ratio			3.5	3.5
Actual financial leverage ratio			2.88	2.88
Remaining borrowing capacity			$ 68,800,000	$ 68,800,000
Minimum permitted fixed charge coverage ratio			1.15	1.15
Actual fixed charge coverage ratio			1.45	1.45
2015 Credit Facility | Insurance Carriers Collateral
Debt Instrument [Line Items]
Letters of credit issued and outstanding			$ 13,700,000	$ 13,700,000
2015 Credit Facility | Work Performance Obligations
Debt Instrument [Line Items]
Letters of credit issued and outstanding			$ 15,600,000	$ 15,600,000
2015 Credit Facility | LIBOR | 2015 Interest Rate Swap
Debt Instrument [Line Items]
Interest rate at period end			4.39%	4.39%
2015 Credit Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate				1.25%
2015 Credit Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate				2.25%
2015 Credit Facility | Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Term				5 years
2015 Credit Facility | Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 300,000,000.0	$ 300,000,000.0
Term of revolving line of credit		5 years
Maximum borrowing capacity, post sale			$ 275,000,000.0	275,000,000.0
Unamortized loan costs				2,400,000
Interest expense, debt				200,000
Proceeds from line of credit, net				$ 16,000,000
Line of Credit
Debt Instrument [Line Items]
Interest rate at period end			4.39%	4.39%		3.50%
Line of credit			$ 19,000,000	$ 19,000,000		$ 38,000,000
2018 Credit Facility
Debt Instrument [Line Items]
Notional amount					$ 170,600,000.0
Bayou
Debt Instrument [Line Items]
Proceeds from divestiture of businesses	$ 46,000,000		$ 35,000,000
Repayment from proceeds from divestiture of businesses				$ (35,000,000)