Business Segment Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Business segment information
Number of reportable segments | segment	2
Revenue	$ 461.4	$ 431.7
Operating Income (loss)	41.9	38.1
Assets	2,242.5		$ 2,128.6
Eliminations
Business segment information
Revenue	(3.2)	(0.9)
Corporate, eliminations and other
Business segment information
Operating Income (loss)	0.2	0.2
Assets	(4.0)		(5.2)
BSI | Operating segments
Business segment information
Revenue	416.8	387.0
Operating Income (loss)	38.6	35.7
Assets	2,192.8		2,100.6
BEST | Operating segments
Business segment information
Revenue	47.8	45.6
Operating Income (loss)	3.1	$ 2.2
Assets	$ 53.7		$ 33.2