Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended							3 Months Ended	1 Months Ended	3 Months Ended		6 Months Ended				1 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Non-qualified stock options granted prior to May 2008	Mar. 31, 2013 Non-qualified stock options granted subsequent to April 2008	Mar. 31, 2013 Fiscal 2011 beginning on October 1, 2010 and ending on September 30, 2013	Mar. 31, 2013 Fiscal 2012 beginning on October 1, 2011 and ending on September 30, 2014	Mar. 31, 2013 Fiscal 2013 beginning on October 1, 2012 and ending on September 30, 2015	Mar. 31, 2013 Minimum	Sep. 30, 2000 Maximum	Mar. 31, 2013 Maximum	Mar. 31, 2012 Maximum	Mar. 31, 2013 Maximum	Mar. 31, 2012 Maximum	Mar. 31, 2013 Nonqualified Stock Options Minimum	Mar. 31, 2013 Nonqualified Stock Options Maximum	Dec. 12, 2012 Restricted Stock Units (RSUs)	Mar. 31, 2013 Restricted Stock Units (RSUs)
Stock Based Compensation Activity [Line Items]
Unrecognized compensation costs related to non-vested awards	$ 4,600,000		$ 4,600,000
Weighted average period for recognition of compensation costs related to non-vested awards	2 years 8 months 12 days
Performance Share Awards Fully Expensed	1,600,000		1,600,000
Weighted average per share fair value of stock options	$ 9.99	$ 5.95	$ 8.69	$ 5.24
Dividend yield	0.00%	0.00%	0.00%	0.00%
Stock option expiration term upon expiration of employment or service																7 years	10 years
Percentage of non-qualified stock options on each of first five anniversaries					20.00%
Percentage of non-qualified stock options on each of first four anniversaries						25.00%
Total pre-tax intrinsic value of options exercised	49,000	49,000	69,000	49,000
Restricted stock expenses												100,000	100,000	100,000	200,000
Expenses recognized related to Performance Shares	400,000	100,000	600,000	300,000
Performance Shares, time period			3 years
Performance period start date							Oct. 01, 2010	Oct. 01, 2011	Oct. 01, 2012
Performance period end date							Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2015
Targeted number of shares to be vested upon achievement of all or portion of performance objectives during the performance period							68,533	62,497	42,753
Performance share awards, estimated vesting percentage										20.00%		200.00%
Common stock authorized, shares											400,000
Annual compensation withheld											10.00%
Annual compensation withheld, maximum limit											25,000
Employee contributions												100,000	100,000	100,000	100,000
Stock compensation expenses recognized												100,000	100,000	100,000	100,000
Number of restricted stock units awarded																		11,776	1,691
Number of restricted stock issued value																			46,000
RSU award vest each year																		33.00%
RSU expenses												$ 100,000		$ 100,000