Long-Term Debt and Credit Facility - Additional Information (Details)	1 Months Ended	6 Months Ended
	Oct. 31, 2015 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Amount retired under prior credit facility	$ 344,700,000
Current maturities of long-term debt		$ 27,210,000		$ 19,835,000
Debt designated as third-party debt		9,600,000		9,600,000
Third-party notes and bank debt held		300,000		300,000
Long-term debt, fair value		$ 380,400,000		366,000,000
2015 Interest Rate Swap
Debt Instrument [Line Items]
Notional Amount	$ 262,500,000
Fixed interest rate	1.46%
2015 Credit Facility
Debt Instrument [Line Items]
Senior secured credit facility	$ 650,000,000
Maximum borrowing capacity	$ 350,000,000
Term of revolving line of credit	5 years
Term of term loan facility	5 years
Interest rate at period end		3.23%
Secured debt outstanding		$ 319,400,000		328,100,000
Proceeds from line of credit, net		53,000,000
Letters of credit issued and outstanding		$ 33,900,000
Line of credit				$ 36,000,000
Portion of amortization of term loan	$ 262,500,000
Initial maximum financial leverage ratio		3.50	3.75
Actual financial leverage ratio		2.90
Remaining borrowing capacity		$ 81,100,000
Minimum permitted fixed charge coverage ratio		1.25
Actual fixed charge coverage ratio		1.83
2015 Credit Facility | Insurance Carriers Collateral
Debt Instrument [Line Items]
Letters of credit issued and outstanding		$ 15,100,000
2015 Credit Facility | Work Performance Obligations
Debt Instrument [Line Items]
Letters of credit issued and outstanding		$ 18,800,000
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%
Line of Credit
Debt Instrument [Line Items]
Interest rate at period end		3.18%		2.96%
Current maturities of long-term debt		$ 3,000,000
Line of credit		53,000,000		$ 36,000,000
Line of Credit | 2015 Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 300,000,000
Proceeds from line of credit, net		$ 17,000,000