Segment Information (Detail 2) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenue recognition
Increase (decrease) in operating income	$ 10,293	$ 19,215	$ 40,678	$ 53,222
Increase (decrease) in net income	$ 8,786	$ 12,216	$ 2,937	$ 36,765
Increase (decrease) in net income per common share (in dollars per share)	$ 0.33	$ 0.46	$ 0.11	$ 1.37
Change in estimated total costs | Adjustment
Revenue recognition
Increase (decrease) in operating income		$ (4,800)	$ (13,800)	$ (3,800)
Increase (decrease) in net income	$ 300	$ (2,000)	$ 10,700	$ (300)
Increase (decrease) in net income per common share (in dollars per share)	$ 0.01	$ 0.07	$ 0.40	$ 0.01