Share-Based Compensation: (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 1.1	$ 0.7	$ 2.9	$ 2.0
Total recognized tax benefit	(0.4)	(0.3)	(1.2)	(0.8)
Share-based expense (net of tax)	0.7	0.4	1.7	1.2
Stock options
Share-based expense (net of estimated forfeitures)
Total share-based expense	0.2	0.2	0.6	0.6
Non-vested stock/Restricted stock units
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 0.9	$ 0.5	$ 2.3	$ 1.4