Benefit Plans - Unfunded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Projected benefit obligation	$ 27,539	$ 30,877	$ 28,914
Fair value of plan assets	20,254	23,461	$ 21,345
Underfunded status	7,285	7,416
Other post-retirement benefits income (loss)	3,494	$ 2,965
Expected amortization, next fiscal year	$ 100