CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands	Total	Common Stock	Paid in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Sep. 30, 2014		27,173
Beginning balance at Sep. 30, 2014	$ 279,118,000	$ 27,000	$ 851,624,000	$ (571,257,000)	$ (1,276,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	344,094,000			344,094,000
Change in unrealized loss related to available-for-sale securities	1,276,000				1,276,000
Total comprehensive income	345,370,000
Conversion of TEU (debt to stock conversion) (in shares)		5,222
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments	1,000	$ 5,000	(4,000)
Amortization of nonvested stock awards	6,135,000		6,135,000
Exercises of stock options (in shares)		1
Exercises of stock options	14,000		14,000
Tax excess (deficiency) from stock transactions	(22,000)		(22,000)
Shares issued under employee stock plans, net (in shares)		410
Shares issued under employee stock plans, net	0		0
Forfeiture of restricted stock (in shares)		(135)
Forfeiture of restricted stock	0
Common stock redeemed (in shares)		(10)
Common stock redeemed	(192,000)		(192,000)
Other activity	(1,000)	$ 1,000	(2,000)
Ending balance (in shares) at Sep. 30, 2015		32,661
Ending balance at Sep. 30, 2015	630,423,000	$ 33,000	857,553,000	(227,163,000)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,693,000			4,693,000
Change in unrealized loss related to available-for-sale securities	0
Total comprehensive income	4,693,000
Amortization of nonvested stock awards	7,959,000		7,959,000
Shares issued under employee stock plans, net (in shares)		491
Shares issued under employee stock plans, net	0	$ 0	0
Forfeiture of restricted stock (in shares)		(64)
Forfeiture of restricted stock	0
Common stock redeemed (in shares)		(17)
Common stock redeemed	(222,000)		(222,000)
Ending balance (in shares) at Sep. 30, 2016		33,071
Ending balance at Sep. 30, 2016	642,853,000	$ 33,000	865,290,000	(222,470,000)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31,813,000			31,813,000
Change in unrealized loss related to available-for-sale securities	0
Total comprehensive income	31,813,000
Amortization of nonvested stock awards	8,164,000		8,164,000
Exercises of stock options (in shares)		2
Exercises of stock options	24,000		24,000
Shares issued under employee stock plans, net (in shares)		536
Shares issued under employee stock plans, net	1,000	$ 1,000
Forfeiture of restricted stock (in shares)		(61)
Forfeiture of restricted stock	0
Common stock redeemed (in shares)		(32)
Common stock redeemed	(415,000)		(415,000)
Ending balance (in shares) at Sep. 30, 2017		33,516
Ending balance at Sep. 30, 2017	$ 682,440,000	$ 34,000	$ 873,063,000	$ (190,657,000)	$ 0