Share-Based Compensation: (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 1.5	$ 1.1	$ 4.3	$ 2.9
Total recognized tax benefit	(0.6)	(0.4)	(1.7)	(1.2)
Share-based expense (net of tax)	0.9	0.7	2.6	1.7
Stock options
Share-based expense (net of estimated forfeitures)
Total share-based expense	0.1	0.2	0.3	0.6
Non-vested stock/Restricted stock units
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 1.4	$ 0.9	$ 4.0	$ 2.3