Equity Incentive Plans - Restricted Stock Units (Details) - USD ($)	1 Months Ended			12 Months Ended
	Mar. 31, 2018	Aug. 31, 2017	Mar. 30, 2017	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Mar. 23, 2018	Mar. 22, 2018	Jan. 31, 2018	Jan. 31, 2017
Weighted-Average Grant Date Fair Value
Aggregate Intrinsic Value									$ 75,500,000
Stock-based compensation expense				$ 150,673,000	$ 116,668,000	$ 58,225,000
Unrecognized compensation cost related to stock awards, weighted-average period				2 years 7 months 6 days
Performance Shares
Weighted-Average Grant Date Fair Value
Stock-based compensation expense				$ 600,000	$ 3,300,000	$ 2,500,000
Restricted stock units
Number of Restricted Stock Units Outstanding
Unvested, beginning balance (in shares)				8,783,024
Granted (in shares)				15,779,364
Vested (in shares)				(5,277,679)
Forfeited (in shares)				(1,602,063)
Unvested, ending balance (in shares)				17,682,646	8,783,024
Weighted-Average Grant Date Fair Value
Unvested, beginning balance (in dollars per share)				$ 13.06
Granted (in dollars per share)				12.16
Vested (in dollars per share)				12.30
Forfeited (in dollars per share)				11.88
Unvested, ending balance (in dollars per share)				$ 12.60	$ 13.06
Aggregate Intrinsic Value									356,117,000	$ 99,863,000
Unrecognized employee compensation cost									$ 187,200,000
Unrecognized compensation cost related to stock awards, weighted-average period				2 years 7 months 6 days
Awards outstanding (in shares)				8,783,024	8,783,024				17,682,646	8,783,024
Granted March 2017 | 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				$ 4,200,000
Unrecognized employee compensation cost									$ 3,300,000
Unrecognized compensation cost related to stock awards, weighted-average period				2 years 2 months 12 days
Granted August 2017 | Performance Shares
Number of Restricted Stock Units Outstanding
Granted (in shares)		464,744
Weighted-Average Grant Date Fair Value
Stock-based compensation expense				$ 0
Minimum | Granted March 2017 | Performance Shares
Weighted-Average Grant Date Fair Value
Award vesting rights, percentage			0.00%
Minimum | Granted August 2017 | Performance Shares
Weighted-Average Grant Date Fair Value
Award vesting rights, percentage		0.00%
Maximum | Granted March 2017 | Performance Shares
Weighted-Average Grant Date Fair Value
Award vesting rights, percentage			150.00%
Maximum | Granted August 2017 | Performance Shares
Weighted-Average Grant Date Fair Value
Award vesting rights, percentage		150.00%
Subsequent Event | Performance Shares
Weighted-Average Grant Date Fair Value
Awards outstanding (in shares)								1,375,210
Subsequent Event | Restricted stock units
Weighted-Average Grant Date Fair Value
Granted (in dollars per share)	$ 21.13
Awards outstanding (in shares)							1,375,210