Benefit Plans - Funded Status of Plan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Change in Projected Benefit Obligation
Projected benefit obligation, beginning of period			$ 32,820	$ 28,624	$ 28,624
Service cost	$ 300	$ 250	900	751	1,001
Interest cost	310	$ 307	931	921	1,228
Actuarial loss			0		2,474
Benefits paid			(396)		(507)
Projected benefit obligation, end of period	34,255		34,255		32,820
Change in Plan Assets
Plan assets at fair value, beginning of period			0	$ 0	0
Company contributions			396		507
Benefits paid			(396)		(507)
Plan assets at fair value, end of period	0		0		0
Unfunded Status of the Plan	$ (34,255)		$ (34,255)		$ (32,820)