Income Taxes - Additional Information (Detail) - USD ($)			3 Months Ended												12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2018		Dec. 31, 2017	[1],[2]	Sep. 30, 2017	[1],[2]	Jun. 30, 2017	[1],[2]	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018		Mar. 31, 2017	Mar. 31, 2016
Income Taxes [Line Items]
U.S. federal statutory corporate tax rate	21.00%	35.00%													31.50%		35.00%	35.00%
Blended U.S. federal statutory corporate income tax rate															31.50%
Income tax provision			$ 11,660,000	[1],[2]	$ 32,208,000		$ 7,981,000		$ (3,582,000)		$ 14,457,000	$ 10,394,000	$ 5,861,000	$ 8,515,000	$ 48,267,000	[1],[2]	$ 39,227,000	$ 27,691,000
Effective income tax rate															30.10%		43.00%	42.10%
Measurement period															1 year
Income tax expense															$ 21,400,000
Valuation allowance			1,652,000								$ 2,468,000				1,652,000		$ 2,468,000
Net operating loss carry forwards			72,200,000												72,200,000
Interest and penalties															$ 0		$ 0	$ 0
Earliest Tax Year
Income Taxes [Line Items]
Net operating loss carry forwards expiration period															2019
Latest Tax Year
Income Taxes [Line Items]
Net operating loss carry forwards expiration period															2035
Foreign
Income Taxes [Line Items]
Net operating loss carry forwards			3,900,000												$ 3,900,000
Federal
Income Taxes [Line Items]
Research and development credit carry forwards			16,600,000												16,600,000
State
Income Taxes [Line Items]
Research and development credit carry forwards			$ 9,000,000												9,000,000
ASU 2016-09
Income Taxes [Line Items]
Excess tax benefits from stock-based awards															$ 31,000,000

[1] In the first quarter of fiscal 2018, the Company adopted Accounting Standards Update No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which requires that all excess tax benefits and tax deficiencies related share-based compensation arrangements be recognized as income tax benefit or expense, instead of in stockholders’ equity as previous guidance required. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018.

[2] On December 22, 2017, the Tax Cuts and Jobs Act, or Tax Reform Act, was enacted into law. This new law, among other items, reduces the U.S. federal statutory corporate income tax rate from 35% to 21% effective January 1, 2018. During the year ended March 31, 2018, the Company recorded tax expense adjustments for $21.4 million related to the revaluation of its deferred taxes due to a reduction of the U.S. federal statutory corporate income tax rate.