Equity Incentive Plans - Restricted Stock Units (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Jan. 31, 2017
Weighted-Average Grant Date Fair Value
Compensation cost, weighted average term	2 years 8 months
Stock-based compensation expense	$ 32,219	$ 22,998
Restricted Stock Units
Number of Restricted Stock Units Outstanding
Unvested, Beginning balance (in shares)	8,783,024
Granted (in shares)	8,014,950
Vested (in shares)	(794,543)
Forfeited (in shares)	(376,522)
Unvested, Ending balance (in shares)	15,626,909
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share)	$ 13.06
Granted (in dollars per share)	10.19
Vested (in dollars per share)	10.38
Forfeited (in dollars per share)	12.18
Ending balance (in dollars per share)	$ 11.74
Aggregate Intrinsic Value	$ 165,802		$ 99,863
Compensation not yet recognized	$ 165,300
Compensation cost, weighted average term	2 years 7 months
Performance Shares
Number of Restricted Stock Units Outstanding
Granted (in shares)	827,000
Weighted-Average Grant Date Fair Value
Stock-based compensation expense	$ 468
Performance Shares | Minimum
Number of Restricted Stock Units Outstanding
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	0.00%
Performance Shares | Maximum
Number of Restricted Stock Units Outstanding
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	150.00%