Employee Benefit Plans - Net Periodic Pension Cost of Defined Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Benefits and Share-based Compensation, Noncash [Abstract]
Service cost	$ 94	$ 35	$ 206	$ 51
Interest cost	18	11	31	21
Amortization of prior service cost	21	21	42	42
Net periodic benefit cost	$ 133	$ 67	$ 279	$ 114