Share-Based Compensation: (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 1.3	$ 0.8
Total recognized tax benefit	(0.5)	(0.3)
Share-based expense (net of tax)	0.8	0.5
Stock options
Share-based expense (net of estimated forfeitures)
Total share-based expense	0.1	0.2
Non-vested stock/Restricted stock units
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 1.2	$ 0.6