Long-Term Debt and Credit Facility - Additional Information (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Mar. 12, 2018 USD ($)	Oct. 31, 2015 USD ($)
Debt Instrument [Line Items]
Fees		$ 2,400,000
Up front lending fees		900,000
Third party arrangement fees		1,500,000
Proceeds from line of credit, net	$ 13,000,000
Third-party notes and bank debt held	900,000		$ 1,000,000
Long-term debt, fair value	$ 323,800,000		307,700,000
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
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 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	275,600,000
Proceeds from line of credit, net	44,000,000
Letters of credit issued and outstanding	$ 22,600,000
Secured debt			282,200,000
Line of credit			$ 31,000,000
Portion of amortization of term loan					$ 262,500,000
Initial maximum financial leverage ratio	3.75
Actual financial leverage ratio	3.23
Remaining borrowing capacity	$ 54,000,000
Minimum permitted fixed charge coverage ratio	1.15
Actual fixed charge coverage ratio	1.35
2015 Credit Facility | Insurance Carriers Collateral
Debt Instrument [Line Items]
Letters of credit issued and outstanding	$ 12,300,000
2015 Credit Facility | Work Performance Obligations
Debt Instrument [Line Items]
Letters of credit issued and outstanding	$ 10,300,000
2015 Credit Facility | LIBOR | 2015 Interest Rate Swap
Debt Instrument [Line Items]
Interest rate at period end	4.49%
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
Debt Instrument [Line Items]
Debt instrument, term	5 years
2015 Credit Facility | Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 275,000,000.0
Term of revolving line of credit	5 years
Unamortized loan costs		2,400,000
Interest expense, debt		$ 200,000
Line of Credit
Debt Instrument [Line Items]
Interest rate at period end	4.49%		4.45%
Line of credit	$ 44,000,000		$ 31,000,000
2018 Credit Facility
Debt Instrument [Line Items]
Notional amount				$ 170,600,000.0