Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Retirement Benefits [Abstract]
Defined benefit plan, expected future employer contributions, current fiscal year	$ 2.0
Defined benefit plan, employer contributions			$ 2.5
Defined contribution plan, compensation expense	$ 0.9	$ 1.2