Stock Incentive Plans - Intrinsic Value Calculated Based on Grant Date Fair Value (Detail) (USD $)	1 Months Ended								2 Months Ended			7 Months Ended	12 Months Ended
	Oct. 31, 2013	Jul. 31, 2012	Jan. 31, 2012	Dec. 31, 2011	Oct. 31, 2011	Jul. 31, 2011	May 31, 2011	Jan. 31, 2011	Oct. 31, 2012	May 31, 2012	Apr. 30, 2011	Jul. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options granted	14,450	7,000	8,500	143,000	75,400	12,500	51,650	26,000	36,800	36,750	73,500	82,815	97,265	89,050	382,050
Intrinsic value calculated based on grant date fair value, Exercise price					$ 10.81			$ 18.80	$ 9.41	$ 9.45	$ 25.61	$ 6.60
Intrinsic value calculated based on grant date fair value, Exercise price	$ 12.11	$ 10.20	$ 9.39	$ 10.19	$ 10.93	$ 16.86	$ 22.92	$ 21.64	$ 9.58	$ 10.43	$ 27.63	$ 7.97
Intrinsic value calculated based on grant date fair value, Intrinsic value per share