Condensed Consolidated 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 and comprehensive loss	(105,980)			(105,980)
Amortization of nonvested stock awards	7,692		7,692
Exercises of stock options (in shares)		8
Exercises of stock options	62		62
Shares issued under employee stock plans, net (in shares)		443
Forfeiture of restricted stock (in shares)		(210)
Common stock redeemed (in shares)		(79)
Common stock redeemed for tax liability	(1,565)		(1,565)
Other activity	18		18
Ending balance (in shares) at Jun. 30, 2018		33,678
Ending balance at Jun. 30, 2018	582,667	$ 34	879,270	(296,637)
Beginning balance (in shares) at Mar. 31, 2018		33,628
Beginning balance at Mar. 31, 2018	566,966	$ 34	876,978	(310,046)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss and comprehensive loss	13,409			13,409
Amortization of nonvested stock awards	2,484		2,484
Exercises of stock options (in shares)		6
Exercises of stock options	49		49
Shares issued under employee stock plans, net (in shares)		66
Forfeiture of restricted stock (in shares)		(6)
Common stock redeemed (in shares)		(16)
Common stock redeemed for tax liability	(241)		(241)
Ending balance (in shares) at Jun. 30, 2018		33,678
Ending balance at Jun. 30, 2018	582,667	$ 34	879,270	(296,637)
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 and comprehensive loss	(81,949)			(81,949)
Amortization of nonvested stock awards	7,993		7,993
Exercises of stock options (in shares)		27
Exercises of stock options	278		278
Shares issued under employee stock plans, net (in shares)		914
Forfeiture of restricted stock (in shares)		(36)
Common stock redeemed (in shares)		(179)
Common stock redeemed for tax liability	(1,889)		(1,889)
Share repurchases (in shares)		(3,200)
Share repurchases	(34,624)	$ (3)	(34,621)
Ending balance (in shares) at Jun. 30, 2019		31,048
Ending balance at Jun. 30, 2019	533,836	$ 31	851,786	(317,981)
Beginning balance (in shares) at Mar. 31, 2019		32,044
Beginning balance at Mar. 31, 2019	529,158	$ 32	858,709	(329,583)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss and comprehensive loss	11,602			11,602
Amortization of nonvested stock awards	3,699		3,699
Shares issued under employee stock plans, net (in shares)		4
Forfeiture of restricted stock (in shares)		(6)
Common stock redeemed (in shares)		0
Common stock redeemed for tax liability	(3)		(3)
Share repurchases (in shares)		(994)
Share repurchases	(10,620)	$ (1)	(10,619)
Ending balance (in shares) at Jun. 30, 2019		31,048
Ending balance at Jun. 30, 2019	$ 533,836	$ 31	$ 851,786	$ (317,981)