SENIOR SECURED REVOLVING CREDIT FACILITY: (Details) (Revolver, USD $) In Millions, unless otherwise specified			9 Months Ended					9 Months Ended
	Sep. 30, 2012	May 08, 2012	Sep. 30, 2012 LIBOR	Sep. 30, 2012 Bank Prime Rate	Sep. 30, 2012 Minimum	Sep. 30, 2012 Minimum LIBOR	Sep. 30, 2012 Minimum Bank Prime Rate	Sep. 30, 2012 Maximum	Sep. 30, 2012 Maximum LIBOR	Sep. 30, 2012 Maximum Bank Prime Rate
Senior Secured Revolving Credit Facility
Maximum borrowing capacity		$ 600
Basis of interest rate			LIBOR	Bank Prime Rate
Interest rate margin (as a percent)						1.75%	0.75%		2.75%	1.75%
Borrowing base	245
Reduction in borrowing base due to issue of letter of credit	$ 48
Commitment fees (as a percent)					0.375%			0.50%