CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
Schedule of Available-for-sale Securities
Maturities and sales of investments	$ 1,692	$ 60,942
Corporate debt securities (available-for-sale)
Schedule of Available-for-sale Securities
Cost basis	1,193
Gross unrealized gains	0
Gross unrealized losses	0
Estimated Fair Value	1,193
Bank time deposits
Schedule of Available-for-sale Securities
Cost basis	7,217		$ 3,184
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	7,217		3,184
Total short-term investments
Schedule of Available-for-sale Securities
Cost basis	8,410		3,184
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	8,410		3,184
Cash and bank time deposits
Schedule of Available-for-sale Securities
Cost basis	349,936		307,188
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	349,936		307,188
Money market funds
Schedule of Available-for-sale Securities
Cost basis	209		175
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	209		175
Commercial paper
Schedule of Available-for-sale Securities
Cost basis	14,993
Gross unrealized gains	0
Gross unrealized losses	0
Estimated Fair Value	14,993
Total cash and cash equivalents
Schedule of Available-for-sale Securities
Cost basis	365,138		307,363
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated Fair Value	$ 365,138		$ 307,363