Commitments and Contingencies - Litigation - Other (Details) $ in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Oct. 31, 2019 USD ($)	Jan. 31, 2020 AUD ($)	Jan. 31, 2020 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Decrease in precious scrap metals	$ 8.5
Offer for compulsory acquisition		$ 48.0
Advance received (as a percentage of total)		90.00%	90.00%
Advance received			$ 31.1
Proceeds from advances, operating			19.2
Proceeds from advances, investing			$ 11.9