Employee Benefit Plans, Projected Benefit Obligation, Accumulated Benefit Obligation and Fair Value of Plan Assets (Details) - Defined Benefit Pension Plans Combined [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Projected Benefit Obligation and Fair Value of Plan Assets [Abstract]
Projected benefit obligation	$ 44,636	$ 40,754	$ 39,469
Fair value of plan assets	41,439	35,467	31,835
Accumulated Benefit Obligation and Fair Value of Plan Assets [Abstract]
Accumulated benefit obligation	41,390	37,822
Fair value of plan assets	$ 41,439	$ 35,467	$ 31,835