Employee Benefits - Benefit Obligation and Plan Assets Deriving Funded Status (Details) - USD ($) $ in Thousands			12 Months Ended
	Sep. 07, 2018	Dec. 19, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in Projected Benefit Obligation
Projected benefit obligation at beginning of year			$ 106,664	$ 105,834
Interest cost			3,882	4,100	$ 4,296
Actuarial gain			(7,371)	4,974
Benefits paid			(7,975)	(8,244)
Projected Benefit Obligation at End of Year			95,200	106,664	105,834
Change in Plan Assets
Fair value of plan assets at beginning of year			87,154	87,711
Actual return on plan assets			2,166	7,687
Employer contributions	$ 20,400		20,420	0
Benefits paid		$ (1,500)	(7,975)	(8,244)
Fair Value of Plan Assets at End of Year			101,765	87,154	$ 87,711
Funded Status			$ 6,565	$ (19,510)