Property and Equipment - Summary of Company's Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,192,866	$ 1,096,017
Less accumulated depreciation and amortization	(315,048)	(310,545)
Property and equipment, net	877,818	785,472
Flight equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,053,640	959,986
Facility & improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	61,246	57,723
Operating equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	24,764	24,594
Data processing equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	32,374	33,870
Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,133	7,867
Medical equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,377	7,079
Other [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,332	$ 4,898