Employee Benefit Plans - Reconciliation of Benefit Obligations, Plan Assets and Funded Status (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension plans
Change in benefit obligation:
Benefit obligation at beginning of plan year			$ 42,898	$ 42,030
Service cost				2	$ 3
Interest cost			305	1,228	1,711
Actuarial loss			(198)	2,940
Benefits paid			(43,005)	(3,302)
Projected benefit obligation at measurement date				42,898	42,030
Change in plan assets:
Fair value of plan assets at beginning of plan year			41,517	42,061
Actual return on plan assets			(1,375)	1,933
Company contribution	$ 1,300	$ 1,600	2,860	825
Benefits paid			(43,002)	(3,302)
Fair value of plan assets at measurement date			0	41,517	42,061
Funded status of the plan:
Benefit obligation in excess of plan assets				(1,381)
Pension liability				(1,381)
Other postretirement benefits
Change in benefit obligation:
Benefit obligation at beginning of plan year			6,073	6,131
Service cost			124	121	137
Interest cost			189	195	257
Actuarial loss			(511)	(180)
Plan participants' contributions			547	564
Benefits paid			(871)	(758)
Projected benefit obligation at measurement date			$ 5,551	$ 6,073	$ 6,131