Benefit Plans - Funded Status of Plan (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Change in Projected Benefit Obligation
Projected benefit obligation, beginning of period	$ 32,474	$ 32,820	$ 32,820
Service cost	250	300	1,200
Interest cost	348	310	1,242
Actuarial loss	0		(2,166)
Benefits paid	(179)		(622)
Projected benefit obligation, end of period	32,893		32,474
Change in Plan Assets
Plan assets at fair value, beginning of period	0	$ 0	0
Company contributions	179		622
Benefits paid	(179)		(622)
Plan assets at fair value, end of period	0		0
Unfunded Status of the Plan	$ (32,893)		$ (32,474)