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Equity Incentive Plans - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 54,229	$ 58,329	$ 174,790	$ 155,938
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		4,400	$ 7,500	19,200	$ 17,700
Unrecognized stock-based compensation expense		$ 21,500		$ 21,500
Compensation cost (in years)				2 years 1 month 6 days
Number of Restricted Stock Outstanding
Unvested, Beginning balance (in shares)				2,267,569
Granted (in shares)				1,399,688
Vested (in shares)				(1,063,977)
Unvested, Ending balance (in shares)	2,267,569	2,603,280		2,603,280
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share)				$ 18.70
Granted (in dollars per share)				20.30
Vested (in dollars per share)				19.32
Ending balance (in dollars per share)	$ 18.70	$ 19.42		$ 19.42
Aggregate Intrinsic Value	$ 40,612	$ 50,660		$ 50,660
Restricted Stock \| Performance Vesting at Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights (as a percent)				100.00%
Number of Restricted Stock Outstanding
Granted (in shares)	183,902			1,291,194
Restricted Stock \| Previously Issued Performance Awards
Number of Restricted Stock Outstanding
Granted (in shares)				108,494
Restricted Stock \| Minimum \| Performance Vesting at Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights (as a percent)				0.00%
Restricted Stock \| Maximum \| Performance Vesting at Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights (as a percent)				160.00%