Stock Based Compensation - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2013	Dec. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Increase in share-based compensation expense	$ 0.8
2011 Long Term Incentive Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Forfeitures benefits			0.4
Long Term Incentive Plan modification expense			0.2
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures		$ 2.7
Executive [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Number of departed employees			2