Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Benefit Plans - Plan Assets Allocation (Details) - Pension Benefits	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Benefit plans
Asset Allocation (as a percent)	100.00%	100.00%
Equity securities
Benefit plans
Asset Allocation (as a percent)	29.00%	32.00%
Target Allocation (as a percent)	30.00%
FHI stock
Benefit plans
Asset Allocation (as a percent)	0.00%	0.00%
BNP Paribas stock
Benefit plans
Asset Allocation (as a percent)	0.00%	0.00%
Debt securities
Benefit plans
Asset Allocation (as a percent)	69.00%	66.00%
Target Allocation (as a percent)	68.00%
Other securities
Benefit plans
Asset Allocation (as a percent)	2.00%	2.00%
Target Allocation (as a percent)	2.00%
Qualified Plan (ERP)
Benefit plans
Expected long term return on plan assets (as a percent)	4.75%	4.75%	5.50%