Subsequent Events (Details) - USD ($) shares in Thousands	Oct. 29, 2018	Oct. 15, 2018	Oct. 01, 2018	Sep. 30, 2018	Sep. 30, 2017
Northern Empire Resources Corp. | Subsequent Event
Subsequent Event [Line Items]
Common stock portion, number of Company stock for each share of Norther Empire stock converted			0
Net assets acquired			$ 63,900,000
Common Stock | Northern Empire Resources Corp. | Subsequent Event
Subsequent Event [Line Items]
Common shares issued (in shares)			12,100
Common Stock | Rye Patch Gold US Inc. | Subsequent Event
Subsequent Event [Line Items]
Common shares issued (value)		$ 19,000,000
Revolving Credit Facility
Subsequent Event [Line Items]
Line of credit facility maximum borrowing capacity					$ 200,000,000.0
Amendment | Revolving Credit Facility | Subsequent Event
Subsequent Event [Line Items]
Increase in line of credit facility	$ 50,000,000
Line of credit facility maximum borrowing capacity	$ 250,000,000.0
Northern Empire Resources Corp.
Subsequent Event [Line Items]
Investment value				$ 4,500,000