Segment Information (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Revenue recognition
Increase (decrease) in operating income	$ 22,177	$ 37,376	$ 34,007	$ 57,885
Increase (decrease) in net income	16,120	29,702	24,549	44,016
Increase (decrease) in net income per common share (in dollars per share)	$ 0.60	$ 1.11	$ 0.91	$ 1.64
Change in estimated total costs | Adjustment
Revenue recognition
Increase (decrease) in operating income	0	3,500	2,500	4,400
Increase (decrease) in net income	$ 0	$ 2,800	$ 2,500	$ 3,700
Increase (decrease) in net income per common share (in dollars per share)		$ 0.11	$ 0.09	$ 0.14