Equity Incentive Plans - Restricted Stock Units (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
Weighted-Average Grant Date Fair Value
Compensation cost, weighted average term			2 years 6 months
Stock-based compensation expense	$ 36,838	$ 27,896	$ 69,057	$ 50,894
Restricted Stock Units
Number of Restricted Stock Units Outstanding
Unvested, Beginning balance (in shares)			8,783,024
Granted (in shares)			9,807,355
Vested (in shares)			(2,221,800)
Forfeited (in shares)			(908,755)
Unvested, Ending balance (in shares)	15,459,824		15,459,824
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share)			$ 13.06
Granted (in dollars per share)			10.59
Vested (in dollars per share)			12.46
Forfeited (in dollars per share)			11.50
Ending balance (in dollars per share)	$ 11.67		$ 11.67
Aggregate Intrinsic Value	$ 186,600		$ 186,600		$ 99,863
Compensation not yet recognized	$ 161,500		$ 161,500
Compensation cost, weighted average term			2 years 7 months
Performance Shares
Number of Restricted Stock Units Outstanding
Granted (in shares)			750,000
Forfeited (in shares)	(77,000)
Weighted-Average Grant Date Fair Value
Stock-based compensation expense	$ 1,200		$ 1,600
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%