Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended																12 Months Ended
	Dec. 31, 2017	Mar. 31, 2020		Dec. 31, 2019	[1]	Sep. 30, 2019	[1]	Jun. 30, 2019	[1]	Mar. 31, 2019		Dec. 31, 2018	[1]	Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2020		Mar. 31, 2019		Mar. 31, 2018
Income Taxes [Line Items]
U.S. federal statutory corporate tax rate	35.00%																	21.00%		21.00%		31.50%
Blended U.S. federal statutory corporate income tax rate																						31.50%
Income tax expense																						$ 21,400,000
Potential repatriation of foreign subsidiary earnings																		100.00%		100.00%
Additional federal income tax expense																		$ 0		$ 500,000
Income tax provision		$ 7,515,000	[1]	$ 27,799,000		$ 4,287,000		$ 14,215,000		$ 24,569,000	[1]	$ 19,648,000		$ 1,706,000		$ (41,579,000)		$ 53,816,000	[1]	$ 4,344,000	[1]	$ 48,267,000
Effective income tax rate																		21.00%		1.60%		30.10%
Valuation allowance		15,170,000								$ 1,302,000								$ 15,170,000		$ 1,302,000
Foreign tax credits																		21,500,000
Interest and penalties on uncertain tax positions																		$ 0		0		$ 0
Earliest Tax Year
Income Taxes [Line Items]
Foreign tax credits carry forwards expiration period																		2025
Federal and state research and development credit carry forwards year of expiration																		2021
Latest Tax Year
Income Taxes [Line Items]
Foreign tax credits carry forwards expiration period																		2030
Federal and state research and development credit carry forwards year of expiration																		2040
Foreign
Income Taxes [Line Items]
Net operating loss carry forwards		24,100,000																$ 24,100,000
Federal
Income Taxes [Line Items]
Research and development credit carry forwards		20,500,000																20,500,000
State
Income Taxes [Line Items]
Research and development credit carry forwards		$ 11,300,000																11,300,000
ASU 2016-09
Income Taxes [Line Items]
Excess tax benefits from stock-based awards																		$ 14,800,000		$ 69,300,000		$ 31,000,000.0

[1]   (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.