Pension Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan [Abstract]
Service cost	$ 302	$ 375	$ 367
Interest cost	1,265	1,201	1,250
Amortization of prior service credits	(193)	(362)	(362)
Recognized net actuarial loss	865	1,525	1,505
Curtailment gain	(416)	0	0
Net periodic benefit cost	$ 1,823	$ 2,739	$ 2,760