Annual report pursuant to Section 13 and 15(d)

Employee Retirement Plans - Multiemployer plans (Details)

v3.8.0.1
Employee Retirement Plans - Multiemployer plans (Details) - NCT - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Employee Retirement Plans      
Contribution to NCT (as a percent of total plan contribution) 1.00%    
Contributions by employer $ 2,319 $ 1,926 $ 1,730