Stock-Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended				0 Months Ended
	Mar. 31, 2013 Employee	Mar. 31, 2013 Restricted Stock Plan	Mar. 31, 2012 Restricted Stock Plan	Mar. 31, 2013 Restricted Stock Plan	Mar. 31, 2012 Restricted Stock Plan	Mar. 31, 2013 Restricted Stock Plan Employee	Mar. 31, 2013 Restricted Stock Plan Non-Employee Director	Dec. 10, 2012 Restricted Stock Plan Key Employees and Non-Employee Directors	Nov. 26, 2012 Restricted Stock Plan Key Employees and Non-Employee Directors	Nov. 20, 2012 Restricted Stock Plan Key Employees and Non-Employee Directors
Stock-Based Compensation
Number of shares of common stock reserved for issuance		400,000		400,000
Award vesting period						3 years	3 years
Period of performance goal based on net income used for determination of vesting period						3 years
Restricted stock plan activity, number of shares
Unvested at beginning of the period (in shares)				111,000
Granted (in shares)				36,050				1,100	3,000	31,950
Forfeited / Canceled (in shares)				(11,400)
Vested (in shares)				(38,500)
Unvested at end of the period (in shares)		97,150		97,150
Expected to vest (in shares)		97,150		97,150
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Unvested at beginning of the period (in dollars per share)				$ 42.32
Granted (in dollars per share)				$ 47.94				$ 48.39	$ 47.62	$ 47.96
Forfeited / Canceled (in dollars per share)				$ 41.84
Vested (in dollars per share)				$ 34.00
Unvested at end of the period (in dollars per share)		$ 47.77		$ 47.77
Expected to vest (in dollars per share)		$ 47.77		$ 47.77
Restricted stock plan activity, other disclosures
Compensation expense		$ 387	$ 419	$ 503	$ 742
Remaining unrecognized compensation expense		$ 2,732		$ 2,732
Weighted average period for recognition				1 year 9 months 7 days
Repurchase of stock from employees	9,993
Average purchase price paid (in dollars per shares)	$ 50.51