Benefit Plans - Changes in Projected Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at the beginning of year		$ 30,877	$ 28,914
Service cost	$ 668	548	614
Interest cost	598	1,107	1,192
Actuarial (gain) loss		(2,917)	1,091
Benefits paid		(2,076)	(934)
Projected benefit obligation at end of year	28,914	27,539	30,877
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets as of the beginning of the period		23,461	21,345
Actual return on plan assets		(1,131)	3,050
Benefits paid		(2,076)	(934)
Fair value of plan assets as of December 31	$ 21,345	$ 20,254	$ 23,461