Employee Benefits - Summary of SERPs and Defined Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Benefits
Balances in Deferred Compensation Plan	$ 21.8	$ 21.2
Value of assets for funding future payouts under the deferred compensation plan	21.1
Contributions to Multiemployer Plans	5.4	5.4	$ 5.3
Change in plan assets
Fair value of plan assets at beginning of year	89.0
Fair value of plan assets at end of year	94.9	89.0
Amounts recognized in the statement of financial position
Noncurrent liabilities	(71.8)	(85.4)
Supplemental Executive Retirement Plans
Change in benefit obligation
Benefit obligation at beginning of year	36.6	48.5
Service cost	0.9	0.8	1.1
Interest cost	1.1	1.1	1.6
Actuarial loss	(0.3)	1.0
Benefits paid	(1.1)	(1.2)
Plan settlements		(13.6)
Benefit obligation at end of year	37.2	36.6	48.5
Funded status
Funded status of the plans	(37.2)	(36.6)
Items not yet recognized as component of net periodic pension expense
Unrecognized net actuarial losses	9.1	10.3
Accumulated other comprehensive loss	9.1	10.3
Amounts recognized in the statement of financial position
Current liabilities	(1.1)	(1.2)
Noncurrent liabilities	(36.1)	(35.4)
Accumulated other comprehensive loss	9.1	10.3
Net amount recognized	(28.1)	(26.3)
Accumulated benefit obligation	32.5	32.6
Components of net periodic benefit cost
Service cost	0.9	0.8	1.1
Interest cost	1.1	1.1	1.6
Settlement loss		3.7	1.0
Amortization of net loss	0.9	0.9	1.4
Net periodic benefit cost	$ 2.9	$ 6.5	$ 5.1
Weighted average assumptions to determine net cost
Discount rate (as a percent)	3.04%	3.36%	3.45%
Rate of compensation increase (as a percent)	6.00%	6.00%	6.00%
Weighted average assumptions to determine benefit obligations
Discount rate (as a percent)	3.82%	3.04%
Rate of compensation increase (as a percent)	6.00%	6.00%
Expected employer contributions during 2019	$ 1.1
Defined Benefit Plans
Change in benefit obligation
Benefit obligation at beginning of year	103.5	$ 95.9
Service cost	1.7	1.5	$ 1.6
Interest cost	3.5	3.7	3.9
Actuarial loss	(9.3)	6.2
Benefits paid	(3.8)	(3.8)
Plan amendments	1.0	0.2
Plan settlements		(0.2)
Benefit obligation at end of year	96.6	103.5	95.9
Change in plan assets
Fair value of plan assets at beginning of year	89.0	73.3
Actual return on plan assets	(4.2)	9.9
Employer contributions	13.9	9.8
Benefits paid	(3.8)	(3.8)
Plan settlements		(0.2)
Fair value of plan assets at end of year	94.9	89.0	73.3
Funded status
Funded status of the plans	(1.7)	(14.5)
Items not yet recognized as component of net periodic pension expense
Unrecognized net actuarial losses	23.2	24.5
Unamortized prior service cost	2.8	2.1
Accumulated other comprehensive loss	26.0	26.6
Amounts recognized in the statement of financial position
Noncurrent liabilities	(1.7)	(14.5)
Accumulated other comprehensive loss	26.0	26.6
Net amount recognized	24.3	12.1
Accumulated benefit obligation	96.6	103.5
Information for defined benefit plans with an accumulated benefit obligation and projected benefit obligation in excess of plan assets
Accumulated benefit obligation	53.0	75.5
Projected benefit obligation	53.0	75.5
Fair value of plan assets	50.1	60.3
Components of net periodic benefit cost
Service cost	1.7	1.5	1.6
Interest cost	3.5	3.7	3.9
Expected return on plan assets	(5.1)	(4.4)	(4.6)
Settlement loss		0.1	0.1
Prior service (credit) cost	0.3	0.3	0.3
Amortization of net loss	1.4	1.5	1.5
Net periodic benefit cost	$ 1.8	$ 2.7	$ 2.8
Weighted average assumptions to determine net cost
Discount rate (as a percent)	3.47%	3.93%	4.13%
Expected long-term rate of return on plan assets (as a percent)	5.66%	6.17%	6.57%
Weighted average assumptions to determine benefit obligations
Discount rate (as a percent)	4.06%	3.47%
Expected long-term rate of return on plan assets (as a percent)	5.66%	6.17%
Expected employer contributions during 2019	$ 0.0
Warehouse, delivery, selling, general and administrative expense | Supplemental Executive Retirement Plans
Components of net periodic benefit cost
Net periodic benefit cost	0.9	$ 0.8	$ 1.1
Warehouse, delivery, selling, general and administrative expense | Defined Benefit Plans
Components of net periodic benefit cost
Net periodic benefit cost	1.7	1.5	1.6
Other expenses, net | Supplemental Executive Retirement Plans
Components of net periodic benefit cost
Net periodic benefit cost	2.0	5.7	4.0
Other expenses, net | Defined Benefit Plans
Components of net periodic benefit cost
Net periodic benefit cost	$ 0.1	$ 1.2	$ 1.2