Property and Equipment - Summary of Company's Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,287,546	$ 1,238,850
Less accumulated depreciation and amortization	(383,569)	(355,321)
Property and equipment, net	903,977	883,529
Flight Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,144,315	1,096,986
Facility & Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	61,187	61,330
Operating Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	25,966	26,004
Data Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	33,881	33,178
Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,567	8,461
Medical Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,963	7,514
Other [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,667	$ 5,377