Equity Incentive Plans, Stock Options Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Option shares outstanding beginning balance (in shares)	433,117	913,508	684,299
Options granted (in shares)			244
Options assumed upon acquisition (in shares)			604,900
Options exercised (shares)	(131,666)	(437,906)	(221,987)
Options canceled (in shares)	(17,111)	(42,485)	(153,948)
Option shares outstanding ending balance (in shares)	284,340	433,117	913,508
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Option shares outstanding beginning balance (in dollars per share)	$ 31.51	$ 33.00	$ 28.41
Options granted (in dollars per shares)			41.09
Options assumed upon acquisition (in dollars per share)			35.03
Options exercised (in dollars per share)	31.75	34.34	25.30
Options canceled (in dollars per share)	34.73	34.26	31.52
Option shares outstanding ending balance (in dollars per share)	31.21	$ 31.51	$ 33.00
Closing price of company's common stock related to calculation of aggregate intrinsic value of stock options (in dollars per share)	$ 91.36
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Total intrinsic value of options exercised related to stock incentive plans	$ 7.4	$ 9.6	$ 4.7
Aggregate intrinsic value of options outstanding related to stock incentive plans	17.1
Aggregate intrinsic value of options exercisable related to stock incentive plans	$ 13.8
Exercisable number of option shares (in shares)	224,022	264,061
Weighted average exercise price per share of exercisable options (in dollars per share)	$ 29.96	$ 29.59
Weighted average fair value per share of stock options granted			$ 8.85