Employee Benefit Plans - Qualified Pension Plan (Narrative) (Details) - Pension plans - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans
Settlement expense	$ (11,700)	$ (8,200)	$ (19,900)	$ (641)	$ (1,510)
Fair value of qualified plan assets			0	41,517	$ 42,061
Benefits paid	$ 1,300	$ 1,600	$ 2,860	$ 825