SHORT-TERM INVESTMENTS: (Tables)

6 Months Ended

Jun. 30, 2015

SHORT-TERM INVESTMENTS:

Schedule of short-term investments

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

	At June 30, 2015			At December 31, 2014
Trading securities	$	569.0		$	333.7
Weighted average interest rate	0.52		%	0.78		%
Available for sale	$	4.3		$	4.9
Weighted average interest rate	0.49		%	0.44		%
Total	$	573.3		$	338.6

Summary of activities in short-term investments

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

	Three months ended						Six months ended
	June 30,						June 30,
	2015			2014			2015			2014
Trading securities:
Interest earned	$	0.2		$	1.1		$	0.5		$	2.5
Unrealized gain (loss) at the end of the period	$	(0.2	)	$	1.7		$	(0.2	)	$	1.7
Available for sale:
Interest earned	(*		)	(*		)	(*		)	(*		)
Investment redeemed	$	0.4		$	0.2		$	0.6		$	0.2

(*) Less than $0.1 million