Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash payments :
Interest paid during the year	$ 22.9	$ 24.3	$ 25.2
Income taxes paid during the year	164.5	217.4	205.4
Non cash investing and financing activities :
Changes in accrued capital expenditures	2.0	4.0	3.3
Gain on contract to repurchase common stock	0.0	0.0	18.1
Charitable contribution of marketable securities	2.0	0.0	0.5
Deposits with broker for securities sold short	8.4	10.8	0.0
Securities sold short	$ 8.2	$ 10.7	$ 0.0