Annual report pursuant to Section 13 and 15(d)

Employee Retirement Plans - Pension expense (Details)

v3.10.0.1
Employee Retirement Plans - Pension expense (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2018
USD ($)
item
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Employee Retirement Plans      
Number of regional multi-employer pension plans in which the entity participates | item 37    
Defined contribution plans $ 7,595 $ 4,089 $ 3,950
Multi-employer plans 11,224 8,677 6,593
Total expense related to participation in retirement plans $ 18,819 $ 12,766 $ 10,543