Employee and Director Stock Plans - Schedule Of Share-based Compensation Options Activity (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Jan. 31, 2019 USD ($) $ / shares shares
Number of Shares
Options outstanding (in shares) | shares	200,000
Assumed from acquisitions (in shares) | shares	700,000
Granted (in shares) | shares	0
Exercised (in shares) | shares	(100,000)
Canceled/Forfeited (in shares) | shares	0
Options outstanding (in shares) | shares	817,100
Weighted average exercise price per share
Options outstanding, beginning balance (in dollars per share) | $ / shares	$ 40.49
Assumed from acquisitions (in dollars per share) | $ / shares	20.82
Granted (in dollars per share) | $ / shares	0
Exercised (in dollars per share) | $ / shares	37.64
Canceled/Forfeited (in dollars per share) | $ / shares	0
Options outstanding, ending balance (in dollars per share) | $ / shares	$ 23.95
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options vested, exercisable and outstanding at January 31, 2019, Number of Shares (in shares) | shares	156,400
Options vested and exercisable as of January 31, 2019 and expected to vest thereafter, Number of Shares (in shares) | shares	800,000
Shares available for grant at January 31, 2019 (in shares) | shares	19,400,000
Options vested and exercisable at January 31, 2019, Weighted average exercise price per share (in dollars per share) | $ / shares	$ 37.10
Options vested and exercisable at January 31, 2019 and expected to vest thereafter, Weighted average exercise price per share (in dollars per share) | $ / shares	$ 23.95
Options vested, exercisable and outstanding, Weighted average remaining contractual term (in years)	7 years 8 months 12 days
Options vested and exercisable at January 31, 2019, Weighted average remaining contractual term (in years)	2 years 7 months 6 days
Options vested and exercisable as of January 31, 2019 and expected to vest thereafter, Weighted average remaining contractual term (in years)	7 years 8 months 12 days
Options vested, exercisable and outstanding at January 31, 2019, Aggregate Intrinsic Value | $	$ 100.7
Options vested and exercisable at January 31, 2019, Aggregate Intrinsic Value | $	17.2
Options vested and exercisable as of January 31, 2019 and expected to vest thereafter, Aggregate Intrinsic Value | $	$ 100.7
Closing stock price (in usd per share) | $ / shares	$ 147.20