SHORT-TERM INVESTMENTS: (Tables)

3 Months Ended

Mar. 31, 2014

SHORT-TERM INVESTMENTS:

Schedule of short-term investments

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

	March 31,			December 31,
	2014			2013
Trading securities	$	267.3		$	202.6
Weighted average interest rate	1.87		%	3.78		%
Available for sale	$	5.7		$	5.7
Weighted average interest rate	0.41		%	0.42		%
Total	$	273.0		$	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 March 31,
	2014			2013
Trading:
Interest earned	$	1.4		$	0.6
Unrealized gain (loss) at the end of the period	$	2.2		$	3.5
Available-for-sale:
Interest earned	(*		)	(*		)
Investment redeemed	$	—		$	—

(*) Less than $0.1 million.