Earnings per Share - Tabular Disclosure (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income (loss)	$ 16,486	$ 13,871
Weighted average common shares outstanding used in computing basic earnings (losses) per share (in shares)	70,183	69,181
Dilutive common stock options and restricted stock units (in shares)	681	689
Weighted average common shares outstanding used in computing diluted earnings (losses) per share (in shares)	70,864	69,870
Basic net income (loss) per share (in dollars per share)	$ 0.23	$ 0.20
Diluted net income per share (in dollars per share)	$ 0.23	$ 0.20