Employee Benefit Plans - Defined Benefit Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans
Amounts included in accumulated other comprehensive loss
Unrecognized actuarial losses (gross)	$ 52,100,000	$ 49,300,000
Unrecognized actuarial losses (net of tax)	41,500,000	39,600,000
Unrecognized prior service cost (gross)	800,000	1,000,000.0
Unrecognized prior service cost (net of tax)	600,000	800,000
Projected benefit obligation
Beginning of year	167,500,000	182,800,000
Service cost	2,800,000	3,100,000	$ 2,600,000
Interest cost	6,100,000	5,500,000	5,300,000
Plan amendments	(100,000)	0
Actuarial (gain)/loss	17,200,000	(10,000,000.0)
Benefits paid	(14,600,000)	(13,900,000)
End of year	178,900,000	167,500,000	182,800,000
Fair value of plan assets
Beginning of year	148,600,000	165,700,000
Actual return on plan assets	20,900,000	(4,600,000)
Benefits paid	(14,600,000)	(13,900,000)
End of year	156,500,000	148,600,000	$ 165,700,000
(Unfunded) funded status end of year	(22,400,000)	(18,900,000)
Accumulated benefit obligation at end of year	178,000,000.0	167,000,000.0
Executive supplemental and director defined benefit pension plans
Projected benefit obligation
Beginning of year	19,600,000
End of year	21,800,000	19,600,000
Fair value of plan assets
Beginning of year	0
Company contributions	1,600,000	1,400,000
End of year	0	0
Accumulated benefit obligation at end of year	$ 20,900,000	$ 19,100,000