Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Additional Information (Details)

v3.8.0.1
Employee Benefit Plans - Additional Information (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Retirement Benefits [Abstract]      
Contributions to employee benefit plans $ 2.9 $ 2.4 $ 1.9
Accrued liabilities related to employee obligations $ 1.2 $ 0.9 $ 0.7