SHORT-TERM INVESTMENTS: (Tables)

12 Months Ended

Dec. 31, 2012

SHORT-TERM INVESTMENTS:

Schedule of short-term investments

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

	At December 31,
	2012			2011
Trading securities	$	127.8		$	514.6
Weighted average interest rate	1.87		%	1.37		%
Available-for-sale	6.5			7.3
Weighted average interest rate	0.43		%	0.58		%
Total	$	134.3		$	521.9

Summary of activities in short-term investments

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

	Years ended December 31,
	2012		2011
Trading:
Interest earned	$	3.1	$	6.0
Unrealized gain (loss) at December 31,	$	2.4	$	(7.6	)
Available-for-sale:
Interest earned	$	0.1	$	0.1
Investment redeemed	$	1.9	$	2.1

Schedule of contractual maturities of the Company's available for sale debt securities

At December 31, 2012 and 2011, contractual maturities of the available-for-sale debt securities are as follows (in millions):

	2012		2011
One year or less	$	0.4	$	0.5
Maturing after one year through five years	—		—
Maturing after five years through ten years	—		0.6
Due after 10 years	6.1		6.2
Total debt securities	$	6.5	$	7.3