Retirement Plans - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Additional cash contribution to SERP and TRP for the remainder of the year	$ 10,700,000
Pension lump-sum payment charge		$ 6,300,000
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Net pension plan obligation	145,500,000
Contributions to plan	0	1,700,000
Additional cash contribution to SERP and TRP for the remainder of the year	3,800,000
Pension lump-sum payment charge	0	6,300,000
SERP
Defined Benefit Plan Disclosure [Line Items]
Contributions to plan	900,000	$ 26,700,000
Additional cash contribution to SERP and TRP for the remainder of the year	6,900,000
Accrued Liabilities | Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Net pension plan obligation	$ 7,900,000