Share-Based Compensation: (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 1.5	$ 0.8	$ 2.8	$ 1.8
Total recognized tax benefit	(0.6)	(0.3)	(1.1)	(0.7)
Share-based expense (net of tax)	0.9	0.5	1.7	1.1
Stock options
Share-based expense (net of estimated forfeitures)
Total share-based expense	0.1	0.2	0.2	0.4
Non-vested stock/Restricted stock units
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 1.4	$ 0.6	$ 2.6	$ 1.4