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, 2016		$ 1,323,827	$ 598	$ 694,564	$ 647,322	$ (18,657)
Balance (in shares) at Sep. 30, 2016			59,890,885
Issuance of common stock, net of shares withheld for taxes		8,627	$ 6	8,621	0	0
Issuance of common stock, net of shares withheld for taxes (Shares)			536,223
Issuance of common stock from secondary offering, net of issuance costs		329,323	$ 73	329,250	0	0
Issuance of common stock from secondary offering, net of issuance costs (Shares)			7,273,750
Stock-based compensation		15,071	$ 0	15,071	0	0
Other comprehensive income (loss)		4,094	0	0	0	4,094
Net income (loss)		100,864	0	0	100,864	0
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		3,539	$ 4	3,535	0	0
Issuance of common stock, net of shares withheld for taxes (Shares)			434,932
Issuance costs related to secondary offering of common stock		(474)	$ 0	(474)	0	0
Stock-based compensation		16,473	0	16,473	0	0
Other comprehensive income (loss)		(2,687)	0	0	0	(2,687)
Net income (loss)		98,626	0	0	98,626	0
Dividends on preferred shares	[1]	(12,978)	0	0	(12,978)	0
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		(354)	$ 4	(358)	0	0
Issuance of common stock, net of shares withheld for taxes (Shares)			438,386
Stock-based compensation		16,360	$ 0	16,360	0	0
Other comprehensive income (loss)		(3,346)	0	0	0	(3,346)
Net income (loss)		(10,612)	0	0	(10,612)	0
Dividends on preferred shares	[1]	(24,000)	0	0	(24,000)	0
Balance at Sep. 30, 2019		$ 1,862,353	$ 685	$ 1,083,042	$ 799,222	$ (20,596)
Balance (in shares) at Sep. 30, 2019			68,574,176

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