Accounting for Share-Based Payments - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Jan. 31, 2020 USD ($) $ / shares shares
Shares
Outstanding, beginning balance, shares (in shares) | shares	2,691
Stock options granted (in shares) | shares	683
Stock options canceled, forfeited or expired (in shares) | shares	(189)
Stock options exercised (in shares) | shares	(842)
Outstanding, ending balance, shares (in shares) | shares	2,343
Stock options vested and expected to vest, shares (in shares) | shares	2,263
Stock options exercisable (in shares) | shares	1,287
Weighted-Average Exercise Price Per Share
Outstanding, beginning balance, weighted-average exercise price per share (in dollars per share) | $ / shares	$ 70.87
Stock options granted, weighted-average exercise price per share (in dollars per share) | $ / shares	108.95
Stock options canceled, forfeited or expired, weighted-average exercise price per share (in dollars per share) | $ / shares	95.79
Stock options exercised, weighted-average exercise price per share (in dollars per share) | $ / shares	54.04
Outstanding, ending balance, weighted-average exercise price per share (in dollars per share) | $ / shares	86.01
Stock options vested and expected to vest, weighted-average exercise price per share (in dollars per share) | $ / shares	85.29
Stock options exercisable, weighted-average exercise price per share (in dollars per share) | $ / shares	$ 72.86
Options, Additional Disclosures
Outstanding, weighted-average remaining term	7 years 5 months 1 day
Outstanding, ending balance, aggregate intrinsic value | $	$ 70,977
Stock options vested and expected to vest, weighted-average remaining term	7 years 4 months 9 days
Stock options vested and expected to vest, aggregate intrinsic value | $	$ 70,136
Stock options exercisable, weighted-average remaining term	6 years 3 months 10 days
Stock options exercisable, aggregate intrinsic value | $	$ 55,834