Condensed Consilidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Sep. 30, 2017		33,516
Beginning balance at Sep. 30, 2017	$ 682,440	$ 34	$ 873,063	$ (190,657)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(119,389)			(119,389)
Amortization of nonvested stock awards	5,208		5,208
Exercises of stock options (in shares)		2
Exercises of stock options	13		13
Shares issued under employee stock plans, net (in shares)		376
Forfeiture of restricted stock (in shares)		204
Common stock redeemed (in shares)		(62)
Common stock redeemed	(1,323)		(1,323)
Other activity	17		17
Ending balance (in shares) at Mar. 31, 2018		33,628
Ending balance at Mar. 31, 2018	566,966	$ 34	876,978	(310,046)
Beginning balance (in shares) at Dec. 31, 2017		33,596
Beginning balance at Dec. 31, 2017	552,781	$ 34	874,351	(321,604)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	11,558			11,558
Amortization of nonvested stock awards	2,598		2,598
Exercises of stock options	13		13
Shares issued under employee stock plans, net (in shares)		42
Forfeiture of restricted stock (in shares)		10
Common stock redeemed	(1)		(1)
Other activity	17		17
Ending balance (in shares) at Mar. 31, 2018		33,628
Ending balance at Mar. 31, 2018	566,966	$ 34	876,978	(310,046)
Beginning balance (in shares) at Sep. 30, 2018		33,522
Beginning balance at Sep. 30, 2018	644,027	$ 34	880,025	(236,032)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(93,551)			(93,551)
Amortization of nonvested stock awards	4,294		4,294
Exercises of stock options (in shares)		27
Exercises of stock options	278		278
Shares issued under employee stock plans, net (in shares)		910
Forfeiture of restricted stock (in shares)		30
Common stock redeemed (in shares)		(179)
Common stock redeemed	$ (1,886)		(1,886)
Share repurchases (in shares)	(2,200)	(2,206)
Share repurchases	$ (24,004)	$ (2)	(24,002)
Ending balance (in shares) at Mar. 31, 2019		32,044
Ending balance at Mar. 31, 2019	529,158	$ 32	858,709	(329,583)
Beginning balance (in shares) at Dec. 31, 2018		32,675
Beginning balance at Dec. 31, 2018	635,109	$ 33	863,797	(228,721)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(100,862)			(100,862)
Amortization of nonvested stock awards	2,180		2,180
Exercises of stock options (in shares)		26
Exercises of stock options	271		271
Forfeiture of restricted stock (in shares)		2
Common stock redeemed (in shares)		(3)
Common stock redeemed	$ (35)		(35)
Share repurchases (in shares)	(700)	(652)
Share repurchases	$ (7,505)	$ (1)	(7,504)
Ending balance (in shares) at Mar. 31, 2019		32,044
Ending balance at Mar. 31, 2019	$ 529,158	$ 32	$ 858,709	$ (329,583)