SHORT-TERM INVESTMENTS: (Tables)

9 Months Ended

Sep. 30, 2014

SHORT-TERM INVESTMENTS:

Schedule of short-term investments

Short-term investments were as follows ($ in millions):

	At September 30,2014			At December 31,2013
Trading securities	$	202.8		$	202.6
Weighted average interest rate	2.36		%	3.78		%
Available-for-sale	$	5.2		$	5.7
Weighted average interest rate	0.42		%	0.42		%
Total	$	208.0		$	208.3

Summary of activities in short-term investments

The following table summarizes the activity of these investments by category (in millions):

	Three months ended						Nine months ended
	September 30,						September 30,
	2014			2013			2014			2013
Trading securities:
Interest earned	$	1.1		$	1.9		$	3.6		$	3.9
Unrealized gain (loss) at the end of the period	1.0			0.1			1.0			0.1
Available-for-sale:
Interest earned	(*		)	(*		)	(*		)	(*		)
Investment redeemed	$	0.3		$	—		$	0.5		$	0.4

(*) Less than $0.1 million