CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Jan. 31, 2018
Schedule of Available-for-sale Securities
Maturities and sales of investments	$ 10,620	$ 5,244
Corporate debt securities (available-for-sale)
Schedule of Available-for-sale Securities
Cost basis			$ 2,002
Gross unrealized gains			0
Gross unrealized losses			0
Estimated Fair Value			2,002
Bank time deposits
Schedule of Available-for-sale Securities
Cost basis	49,434		4,564
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	49,434		4,564
Total short-term investments
Schedule of Available-for-sale Securities
Cost basis	49,434		6,566
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	49,434		6,566
Cash and bank time deposits
Schedule of Available-for-sale Securities
Cost basis	297,540		337,756
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	297,540		337,756
Money market funds
Schedule of Available-for-sale Securities
Cost basis	52,640		186
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	52,640		186
Commercial Paper
Schedule of Available-for-sale Securities
Cost basis	3,242
Gross unrealized gains	0
Gross unrealized losses	0
Estimated Fair Value	3,242
Total cash and cash equivalents
Schedule of Available-for-sale Securities
Cost basis	353,422		337,942
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	$ 353,422		$ 337,942