Pension Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Retirement Benefits [Abstract]
Service cost	$ 169	$ 151	$ 338	$ 302
Interest cost on projected benefit obligation	701	693	1,403	1,387
Expected return on plan assets	(1,354)	(1,325)	(2,709)	(2,650)
Net amortization and deferral	672	794	1,344	1,587
Net periodic pension cost	$ 188	$ 313	$ 376	$ 626