Commitments and contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			0 Months Ended	3 Months Ended	12 Months Ended
	Sep. 30, 2014 Cases Lawsuits	Sep. 30, 2011 Cases	Jun. 30, 2014 Lawsuits	May 06, 2014 AA And Saba Consultants [Member]	Dec. 31, 2013 AA And Saba Consultants [Member]	Dec. 31, 2012 AA And Saba Consultants [Member]	Feb. 28, 2014 AA And Saba Consultants [Member]
Loss Contingencies [Line Items]
Number of lawsuits against Company			16
Number of active product liability cases	16	55
Amount of settlement offer						$ 0.8
Verdict against the company							3.3
Loss contingency loss in period					2.6
Amount of attorneys' fees, costs and expenses awarded to plaintiff				$ 1.2