Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Sep. 30, 2017		$ 1,781,806	$ 677	$ 1,047,506	$ 748,186	$ (14,563)
Balance (in shares) at Sep. 30, 2017			67,700,858
Issuance of common stock, net of shares withheld for taxes		2,976	$ 4	2,972
Issuance of common stock, net of shares withheld for taxes (Shares)			404,255
Issuance costs related to secondary offering of common stock		(474)		(474)
Stock-based compensation		13,133		13,133
Other comprehensive income (loss)		(3,506)				(3,506)
Net income (loss)		50,316			50,316
Dividends on preferred shares	[1]	(6,000)			(6,000)
Balance at Jun. 30, 2018		1,838,251	$ 681	1,063,137	792,502	(18,069)
Balance (in shares) at Jun. 30, 2018			68,105,113
Balance at Mar. 31, 2018		1,783,521	$ 680	1,056,248	743,127	(16,534)
Balance (in shares) at Mar. 31, 2018			68,043,284
Issuance of common stock, net of shares withheld for taxes		1,592	$ 1	1,591
Issuance of common stock, net of shares withheld for taxes (Shares)			61,829
Stock-based compensation		5,298		5,298
Other comprehensive income (loss)		(1,535)				(1,535)
Net income (loss)		49,375			49,375
Balance at Jun. 30, 2018		1,838,251	$ 681	1,063,137	792,502	(18,069)
Balance (in shares) at Jun. 30, 2018			68,105,113
Balance at Sep. 30, 2018		1,884,305	$ 681	1,067,040	833,834	(17,250)
Balance (in shares) at Sep. 30, 2018			68,135,790
Issuance of common stock, net of shares withheld for taxes		(1,985)	$ 3	(1,988)
Issuance of common stock, net of shares withheld for taxes (Shares)			344,961
Stock-based compensation		12,901		12,901
Other comprehensive income (loss)		(848)				(848)
Net income (loss)		(37,992)			(37,992)
Dividends on preferred shares	[1]	(18,000)			(18,000)
Balance at Jun. 30, 2019		1,838,381	$ 684	1,077,953	777,842	(18,098)
Balance (in shares) at Jun. 30, 2019			68,480,751
Balance at Mar. 31, 2019		1,807,142	$ 684	1,073,243	752,855	(19,640)
Balance (in shares) at Mar. 31, 2019			68,475,871
Issuance of common stock, net of shares withheld for taxes		73		73
Issuance of common stock, net of shares withheld for taxes (Shares)			4,880
Stock-based compensation		4,637		4,637
Other comprehensive income (loss)		1,542				1,542
Net income (loss)		30,987			30,987
Dividends on preferred shares	[1]	(6,000)			(6,000)
Balance at Jun. 30, 2019		$ 1,838,381	$ 684	$ 1,077,953	$ 777,842	$ (18,098)
Balance (in shares) at Jun. 30, 2019			68,480,751

[1] Amount represents dividends that have been declared and paid during the respective periods presented.