Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	May 31, 2018
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Other-than-temporarily impaired investments	$ 0	$ 0
Gross value of capitalized internal use software	6,000,000	5,700,000	$ 4,900,000
Stock-based compensation costs	800,000	900,000	900,000
Amortization expense	4,100,000	6,100,000	6,900,000
Net book value of capitalized software	10,600,000	9,600,000
Impairment of long-lived assets	0	0	0
Goodwill impairment	$ 0
Computers and Software
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful life	3 years
Other Office Equipment and Site-related Computer Hardware
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful life	3 years
Furniture and Fixtures
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful life	5 years
Capitalized Software Development Costs
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful life	3 years
Sales and marketing
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Advertising expense	$ 19,300,000	$ 17,700,000	$ 21,700,000
Convertible Debt | Convertible Senior Notes Due 2023
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Stated interest rate				0.50%	0.50%