Commitments and Contingencies Diamond Sourcing Activities (Details) (USD $)	12 Months Ended	1 Months Ended	12 Months Ended
	Jan. 31, 2015	Mar. 31, 2011	Jan. 31, 2014	Jan. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Description of Variable Rate Basis	LIBOR
Loans Receivable, Basis Spread on Variable Rate	3.50%
Loans Receivable Fixed Rate	4.00%
Diamond Purchase Commitments Amount Committed	$ 160,000,000
Koidu Limited [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Commitments, Variable Rates		50,000,000
Other diamond mining and exploration companies [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Commitments, Variable Rates			$ 3,050,000	$ 8,015,000