Commitments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Jan. 31, 2014 Aircraft Lessor	Apr. 30, 2013 Aircraft Lessor
Commitments and Contingencies [Line Items]
Number of lessors	19	18
Number of aircraft	165	166
Commitment to purchase	33
Total expenditure	$ 878.1
Helicopter Parts
Commitments and Contingencies [Line Items]
Total expenditure	66.5
Long Term Purchase Commitment, Date	Oct. 31, 2015
Helicopter Parts | Additional purchase commitment
Commitments and Contingencies [Line Items]
Total expenditure	$ 100.0
Long Term Purchase Commitment, Date	Dec. 31, 2016