Calculation of Weighted Average Common Shares and Common Equivalent Shares Outstanding (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net earnings available to common stockholders	$ 22,013	$ 8,685
Weighted average number of common share equivalents:
Common shares used in basic earnings per share	12,827,918	12,704,538
Common share equivalents outstanding related to stock options	98,896	130,558
Total weighted average common shares and common share equivalents used in diluted earnings per share	12,926,814	12,835,096
Basic earnings per common share	$ 1.72	$ 0.68
Diluted earnings per common share	$ 1.70	$ 0.68