Calculation of Weighted Average Common Shares and Common Equivalent Shares Outstanding (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net earnings available to common stockholders	$ 16,991	$ 10,736	$ 55,873	$ 30,851
Weighted average number of common share equivalents:
Common shares used in basic earnings per share	12,911,316	12,748,166	12,873,677	12,726,252
Common share equivalents outstanding related to stock options	71,006	134,282	69,428	126,118
Total weighted average common shares and common share equivalents used in diluted earnings per share	12,982,322	12,882,448	12,943,105	12,852,370
Basic earnings per common share	$ 1.32	$ 0.84	$ 4.34	$ 2.42
Diluted earnings per common share	$ 1.31	$ 0.83	$ 4.32	$ 2.40