Business Segment Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Business segment information
Number of reportable segments | segment	2
Revenue	$ 431.7	$ 384.9
Operating Income (loss)	38.1	37.6
Assets	1,830.5		$ 1,948.5
Eliminations
Business segment information
Revenue	(0.9)	(1.6)
Corporate, eliminations and other
Business segment information
Operating Income (loss)	0.2
Assets	(2.8)		(4.9)
BSI | Operating segments
Business segment information
Revenue	387.0	346.4
Operating Income (loss)	35.7	38.1
Assets	1,796.6		1,917.8
BEST | Operating segments
Business segment information
Revenue	45.6	40.1
Operating Income (loss)	2.2	$ (0.5)
Assets	$ 36.7		$ 35.6