Property and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Summary of Company's property and equipment
Property and equipment, gross	$ 1,038,047	$ 926,678
Less accumulated depreciation and amortization	(288,546)	(266,922)
Property and equipment, net	749,501	659,756
Flight equipment [Member]
Summary of Company's property and equipment
Property and equipment, gross	908,464	811,758
Facility and Improvements [Member]
Summary of Company's property and equipment
Property and equipment, gross	54,407	45,813
Operating equipment [Member]
Summary of Company's property and equipment
Property and equipment, gross	23,929	22,275
Data processing equipment [Member]
Summary of Company's property and equipment
Property and equipment, gross	31,956	29,739
Vehicles [Member]
Summary of Company's property and equipment
Property and equipment, gross	7,595	7,402
Medical equipment [Member]
Summary of Company's property and equipment
Property and equipment, gross	6,991	5,739
Other [Member]
Summary of Company's property and equipment
Property and equipment, gross	$ 4,705	$ 3,952