Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balances at Sep. 30, 2011	$ 538,427	$ 462	$ 248,260	$ 293,110	$ (3,405)
Beginning Balances (in shares) at Sep. 30, 2011		46,154,107
Issuance of common stock (in shares)	1,508,544	1,513,040
Issuance of common stock	24,066	15	24,051
Stock-based compensation	7,873		7,873
Net income	75,565			75,565
Foreign currency translation adjustment	5,283				5,283
Unrealized gain on financial derivatives, net	748				748
Ending Balances at Sep. 30, 2012	651,962	477	280,184	368,675	2,626
Ending Balances (in shares) at Sep. 30, 2012		47,667,147
Issuance of common stock (in shares)	1,189,010	1,231,475
Issuance of common stock	23,523	11	23,512
Stock-based compensation	9,266		9,266
Net income	72,607			72,607
Foreign currency translation adjustment	(4,401)				(4,401)
Unrealized gain on financial derivatives, net	1,399				1,399
Ending Balances at Sep. 30, 2013	754,356	488	312,962	441,282	(376)
Ending Balances (in shares) at Sep. 30, 2013		48,898,622
Issuance of common stock (in shares)	430,310	494,152
Issuance of common stock	7,680	5	7,675
Stock-based compensation	7,422		7,422
Net income	53,846			53,846
Foreign currency translation adjustment	(7,175)				(7,175)
Unrealized gain on financial derivatives, net	972				972
Ending Balances at Sep. 30, 2014	$ 817,101	$ 493	$ 328,059	$ 495,128	$ (6,579)
Ending Balances (in shares) at Sep. 30, 2014		49,392,774