Equity Incentive Plans - Restricted Stock Units (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Aug. 31, 2017	Mar. 30, 2017	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Jan. 31, 2017
Weighted-Average Grant Date Fair Value
Compensation cost, weighted average term					2 years 8 months 12 days
Stock-based compensation expense			$ 38,863,000	$ 28,235,000	$ 107,920,000	$ 79,129,000
Restricted Stock Units
Number of Restricted Stock Units Outstanding
Unvested, Beginning balance (in shares)					8,783,024
Granted (in shares)					14,315,164
Vested (in shares)					(3,627,367)
Forfeited (in shares)					(1,292,330)
Unvested, Ending balance (in shares)			18,178,491		18,178,491
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share)					$ 13.06
Granted (in dollars per share)					11.65
Vested (in dollars per share)					12.33
Forfeited (in dollars per share)					11.75
Ending balance (in dollars per share)			$ 12.21		$ 12.21
Aggregate Intrinsic Value			$ 298,674,000		$ 298,674,000		$ 99,863,000
Compensation not yet recognized			191,600,000		$ 191,600,000
Compensation cost, weighted average term					2 years 7 months
Performance Shares | Granted March 2017
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			1,300,000		$ 2,900,000
Performance Shares | Granted March 2017 | Minimum
Weighted-Average Grant Date Fair Value
Vesting rights, percentage of target number granted		0.00%
Performance Shares | Granted March 2017 | Maximum
Weighted-Average Grant Date Fair Value
Vesting rights, percentage of target number granted		150.00%
Performance Shares | Granted August 2017
Number of Restricted Stock Units Outstanding
Granted (in shares)	464,744
Weighted-Average Grant Date Fair Value
Stock-based compensation expense			$ 0		$ 0
Performance Shares | Granted August 2017 | Minimum
Weighted-Average Grant Date Fair Value
Vesting rights, percentage of target number granted	0.00%
Performance Shares | Granted August 2017 | Maximum
Weighted-Average Grant Date Fair Value
Vesting rights, percentage of target number granted	120.00%