FLEET TRANSITION AND RESTRUCTURING RELATED EXPENSES (DETAILS) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010 positions	Dec. 31, 2009
Restructuring Cost and Reserve [Line Items]
Restructuring, Settlement and Impairment Provisions	$ 38.9	$ 13.2	$ 44.6
Positions Horizon eliminated in the maintenace division (in positions)		100
Cash payment of their accrued sick leave balance multiplied by their hourly rate, percent			25.00%
Horizon Fleet Transition - CRJ-700 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring, Settlement and Impairment Provisions	28.3	10.3	0
Horizon Fleet Transition - Q200 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring, Settlement and Impairment Provisions	10.6	0	8.8
Horizon Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring, Settlement and Impairment Provisions	0	2.9	0
Alaska New Pilot Contract Transition [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring, Settlement and Impairment Provisions	$ 0	$ 0	$ 35.8