Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Fair Value Measurements (Detail)

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Summary of Significant Accounting Policies - Fair Value Measurements (Detail)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Jul. 20, 2017
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Aggregate maximum payout amount $ 157,300 $ 157,300      
Charge associated with disposition of construction barge   3,300 $ 1,900    
Acquisitions 2018          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Contingent consideration 2,800 2,800      
Acquisitions 2018          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Aggregate maximum payout amount 18,000 18,000      
Contingent consideration 16,471 16,471      
Stronghold          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Aggregate maximum payout amount         $ 100,000
Contingent consideration     $ 51,084   $ 51,100
Level 3          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Change in the fair value of contingent consideration liabilities (1,400) (7,700)      
Contingent consideration 74,300 74,300   $ 65,700  
Level 3 | Acquisition Without Maximum Earn-out          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Contingent consideration $ 1,000 $ 1,000      
Volatility | Level 3 | Minimum          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Expected volatility rate 0.230 0.230      
Volatility | Level 3 | Maximum          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Expected volatility rate 0.300 0.300      
Discount Rate | Level 3 | Minimum          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Expected volatility rate 0.021 0.021      
Discount Rate | Level 3 | Maximum          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Expected volatility rate 0.036 0.036