Business Segment Information - Information by Segment (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business segment information
Number of reportable segments | segment									2
Revenue	$ 553.6	$ 466.6	$ 443.7	$ 431.7	$ 530.5	$ 435.6	$ 414.9	$ 384.9	$ 1,895.6	$ 1,765.9	$ 1,611.3
Operating Income (loss)	106.4	$ 69.1	$ 48.8	$ 38.1	95.3	$ 51.3	$ 35.3	$ 37.6	262.4	219.5	181.8
Impairment of assets									0.6	1.1	0.8
Assets	2,128.6				1,948.5				2,128.6	1,948.5
Capital Expenditures									49.2	43.7	37.1
Depreciation and Amortization									64.9	63.9	54.3
Eliminations
Business segment information
Revenue									(6.2)	(9.2)	(11.5)
Corporate, eliminations and other
Business segment information
Operating Income (loss)										(1.3)	1.7
Assets	(5.2)				(4.9)				(5.2)	(4.9)
BSI
Business segment information
Capital Expenditures									42.8	38.5	34.6
Depreciation and Amortization									60.2	59.8	51.3
BSI | Operating segments
Business segment information
Revenue									1,707.0	1,583.9	1,492.6
Operating Income (loss)									247.9	213.4	173.5
Assets	2,100.6				1,917.8				2,100.6	1,917.8
BEST
Business segment information
Capital Expenditures									6.4	5.2	2.5
Depreciation and Amortization									4.7	4.1	3.0
BEST | Operating segments
Business segment information
Revenue									194.8	191.2	130.2
Operating Income (loss)									14.5	7.4	$ 6.6
Assets	$ 33.2				$ 35.6				$ 33.2	$ 35.6