Basis of Presentation and Summary of Significant Accounting Policies - Accelerated Share Repurchase Agreements (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Accelerated Share Repurchases [Line Items]
Agreement Amount		$ 50.0
Settlement Date - December 2018
Accelerated Share Repurchases [Line Items]
Agreement Amount	$ 16.5
Initial Shares Delivered	1.3
Additional Shares Delivered	0.3
Total Shares Delivered	1.6
Average price per share (in dollars per share)	$ 10.62
Settlement Date - July 2019
Accelerated Share Repurchases [Line Items]
Agreement Amount	$ 10.0
Initial Shares Delivered	0.9
Additional Shares Delivered	0.1
Total Shares Delivered	1.0
Average price per share (in dollars per share)	$ 9.87