Summary of Unaudited Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2020		Mar. 31, 2019		Mar. 31, 2018
Disclosure Unaudited Quarterly Financial Information [Abstract]
Revenue	$ 206,658		$ 221,584		$ 204,974		$ 207,666		$ 207,081		$ 200,563		$ 181,778		$ 180,010		$ 840,883		$ 769,432		$ 593,749
Cost of revenue	39,369		39,996		34,867		37,073		34,848		34,023		29,846		30,850		151,305		129,567		98,581
Other operating expenses	109,237		111,329		109,925		109,868		106,844		104,185		101,612		102,412		440,359		415,053
Other income (loss)	(18,739)	[1]	26,757	[1]	(42,824)	[1]	42,413	[1]	33,141	[1]	2,155	[1]	1,513	[1]	1,739	[1]	7,606	[1]	38,548	[1]	3,300
Income before income taxes	39,313		97,016		17,358		103,138		98,530		64,510		51,833		48,487		256,825		263,360		160,437
Income tax provision (benefit)	7,515	[2]	27,799	[2]	4,287	[2]	14,215	[2]	24,569	[2]	19,648	[2]	1,706	[2]	(41,579)	[2]	53,816	[2]	4,344	[2]	48,267
Net income	$ 31,798		$ 69,217		$ 13,071		$ 88,923		$ 73,961		$ 44,862		$ 50,127		$ 90,066		$ 203,009		$ 259,016		$ 112,170
Basic net income per share	$ 0.71		$ 1.53		$ 0.29		$ 1.97		$ 1.64		$ 1.00		$ 1.11		$ 2.02		$ 4.49		$ 5.77		$ 2.54
Diluted net income per share	$ 0.70		$ 1.51		$ 0.28		$ 1.93		$ 1.60		$ 0.97		$ 1.09		$ 1.95		$ 4.43		$ 5.61		$ 2.45

[1]   (1) In fiscal 2019, the Company invested $25.0 million in medical device company Shockwave Medical. The fair value of this investment as of March 31, 2020 was $55.7 million and the Company recognized a pre-tax loss of $0.5 million for the year ended March 31, 2020 and a pre-tax gain of $32.0 million for the year ended March 31, 2019 in other (expense) income, net.

[2]   (2) The income tax provision for the years ended March 31, 2020 and 2019 included excess tax benefits of $14.8 million and $69.3 million, respectively. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the years ended March 31, 2020 and 2019.