SHORT-TERM INVESTMENTS: (Tables)

6 Months Ended

Jun. 30, 2016

SHORT-TERM INVESTMENTS:

Schedule of short-term investments

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

	At June 30, 2016			At December 31, 2015
Trading securities	$	95.4		$	600.2
Weighted average interest rate	1.41		%	0.71		%
Available-for-sale	$	2.8		$	3.3
Weighted average interest rate	0.89		%	0.72		%
Total	$	98.2		$	603.5

Summary of activities of 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,
	2016			2015			2016			2015
Trading securities:
Interest earned	$	0.3		$	0.2		$	0.7		$	0.5
Unrealized gain (loss) at the end of the period	$	0.4		$	(0.2	)	$	0.4		$	(0.2	)
Available-for-sale:
Interest earned	(*		)	(*		)	(*		)	(*		)
Investment redeemed	$	0.2		$	0.4		$	0.5		$	0.6

(*) Less than $0.1 million