Benefit Plans - Summary of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Service cost	$ 352	$ 661	$ 1,884
Interest	146	165	318
Expected return on assets	0	0	(138)
Amortization of prior service costs	(32)	22	279
Recognition of actuarial items	102	(261)	0
Curtailment gain	(47)	(153)	0
Net periodic benefit cost	$ 521	$ 434	$ 2,343