Pension - Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 189	$ 392	$ 381	$ 741
Interest cost	259	336	519	636
Expected return on plan assets	(229)	(290)	(461)	(549)
Prior service cost	(25)	(18)	(50)	(39)
Unrecognized net actuarial loss	14	84	29	168
Net periodic pension cost	$ 208	$ 504	$ 418	$ 957